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 $224.95   8.155%   $243.2947   $243.29   $243.30   $243.30  
  Purchase #2 $160.98   10.352%   $177.6446   $177.64   $177.65   $177.60  
  Purchase #3 $246.92   8.540%   $268.007   $268.01   $268.00   $268.00  
  Purchase #4 $84.53   7.230%   $90.6415   $90.64   $90.65   $90.60  
  Purchase #5 $225.45   12.839%   $254.3955   $254.40   $254.40   $254.40  
  Purchase #6 $212.95   4.593%   $222.7308   $222.73   $222.75   $222.70  
  Purchase #7 $16.30   8.393%   $17.6681   $17.67   $17.65   $17.70  
  7 purchase totals = $1,172.08       $1,274.3822   $1,274.38   $1,274.40   $1,274.30