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 $52.78   11.756%   $58.9848   $58.98   $59.00   $59.00  
  Purchase #2 $165.36   8.117%   $178.7823   $178.78   $178.80   $178.80  
  Purchase #3 $69.82   13.818%   $79.4677   $79.47   $79.45   $79.50  
  Purchase #4 $35.68   13.571%   $40.5221   $40.52   $40.50   $40.50  
  Purchase #5 $211.87   12.519%   $238.394   $238.39   $238.40   $238.40  
  Purchase #6 $155.48   3.581%   $161.0477   $161.05   $161.05   $161.00  
  Purchase #7 $12.97   10.581%   $14.3424   $14.34   $14.35   $14.30  
  7 purchase totals = $703.96       $771.5410   $771.53   $771.55   $771.50