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 $55.94   13.699%   $63.6032   $63.60   $63.60   $63.60  
  Purchase #2 $53.97   12.344%   $60.6321   $60.63   $60.65   $60.60  
  Purchase #3 $178.86   4.122%   $186.2326   $186.23   $186.25   $186.20  
  Purchase #4 $211.33   5.381%   $222.7017   $222.70   $222.70   $222.70  
  Purchase #5 $83.68   12.723%   $94.3266   $94.33   $94.35   $94.30  
  Purchase #6 $212.85   3.114%   $219.4781   $219.48   $219.50   $219.50  
  Purchase #7 $68.33   7.142%   $73.2101   $73.21   $73.20   $73.20  
  7 purchase totals = $864.96       $920.1844   $920.18   $920.25   $920.10