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 $69.73   5.246%   $73.388   $73.39   $73.40   $73.40  
  Purchase #2 $217.81   4.748%   $228.1516   $228.15   $228.15   $228.20  
  Purchase #3 $136.30   8.335%   $147.6606   $147.66   $147.65   $147.70  
  Purchase #4 $238.68   6.427%   $254.02   $254.02   $254.00   $254.00  
  Purchase #5 $243.28   11.764%   $271.8995   $271.90   $271.90   $271.90  
  Purchase #6 $46.95   10.506%   $51.8826   $51.88   $51.90   $51.90  
  Purchase #7 $239.51   12.169%   $268.656   $268.66   $268.65   $268.70  
  7 purchase totals = $1,192.26       $1,295.6583   $1,295.66   $1,295.65   $1,295.80