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 $182.49   10.208%   $201.1186   $201.12   $201.10   $201.10  
  Purchase #2 $177.58   9.365%   $194.2104   $194.21   $194.20   $194.20  
  Purchase #3 $120.91   5.129%   $127.1115   $127.11   $127.10   $127.10  
  Purchase #4 $143.40   5.806%   $151.7258   $151.73   $151.75   $151.70  
  Purchase #5 $242.29   7.692%   $260.9269   $260.93   $260.95   $260.90  
  Purchase #6 $243.41   11.249%   $270.7912   $270.79   $270.80   $270.80  
  Purchase #7 $108.28   8.199%   $117.1579   $117.16   $117.15   $117.20  
  7 purchase totals = $1,218.36       $1,323.0423   $1,323.05   $1,323.05   $1,323.00