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 $45.57   6.616%   $48.5849   $48.58   $48.60   $48.60  
  Purchase #2 $48.38   9.424%   $52.9393   $52.94   $52.95   $52.90  
  Purchase #3 $17.92   4.757%   $18.7725   $18.77   $18.75   $18.80  
  Purchase #4 $203.31   4.268%   $211.9873   $211.99   $212.00   $212.00  
  Purchase #5 $134.25   4.146%   $139.816   $139.82   $139.80   $139.80  
  Purchase #6 $148.34   4.527%   $155.0554   $155.06   $155.05   $155.10  
  Purchase #7 $111.47   10.208%   $122.8489   $122.85   $122.85   $122.80  
  7 purchase totals = $709.24       $750.0043   $750.01   $750.00   $750.00