Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $146.99   5.802%   $155.5184   $155.52   $155.50   $155.50  
  Purchase #2 $239.57   11.308%   $266.6606   $266.66   $266.65   $266.70  
  Purchase #3 $217.62   7.335%   $233.5824   $233.58   $233.60   $233.60  
  Purchase #4 $249.56   6.222%   $265.0876   $265.09   $265.10   $265.10  
  Purchase #5 $134.71   9.753%   $147.8483   $147.85   $147.85   $147.80  
  Purchase #6 $192.96   9.584%   $211.4533   $211.45   $211.45   $211.50  
  Purchase #7 $148.48   13.602%   $168.6762   $168.68   $168.70   $168.70  
  7 purchase totals = $1,329.89       $1,448.8268   $1,448.83   $1,448.85   $1,448.90