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 $244.82   11.705%   $273.4762   $273.48   $273.50   $273.50  
  Purchase #2 $208.53   10.129%   $229.652   $229.65   $229.65   $229.70  
  Purchase #3 $82.86   6.152%   $87.9575   $87.96   $87.95   $88.00  
  Purchase #4 $230.83   7.856%   $248.964   $248.96   $248.95   $249.00  
  Purchase #5 $36.53   13.256%   $41.3724   $41.37   $41.35   $41.40  
  Purchase #6 $230.41   10.506%   $254.6169   $254.62   $254.60   $254.60  
  Purchase #7 $177.58   8.283%   $192.289   $192.29   $192.30   $192.30  
  7 purchase totals = $1,211.56       $1,328.3280   $1,328.33   $1,328.30   $1,328.50