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 $44.77   13.131%   $50.6487   $50.65   $50.65   $50.60  
  Purchase #2 $196.80   7.552%   $211.6623   $211.66   $211.65   $211.70  
  Purchase #3 $75.72   8.484%   $82.1441   $82.14   $82.15   $82.10  
  Purchase #4 $104.27   8.441%   $113.0714   $113.07   $113.05   $113.10  
  Purchase #5 $148.87   6.561%   $158.6374   $158.64   $158.65   $158.60  
  Purchase #6 $145.79   10.351%   $160.8807   $160.88   $160.90   $160.90  
  Purchase #7 $50.45   5.217%   $53.082   $53.08   $53.10   $53.10  
  7 purchase totals = $766.67       $830.1266   $830.12   $830.15   $830.10