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 $75.98   9.212%   $82.9793   $82.98   $83.00   $83.00  
  Purchase #2 $101.75   6.153%   $108.0107   $108.01   $108.00   $108.00  
  Purchase #3 $10.96   3.121%   $11.3021   $11.30   $11.30   $11.30  
  Purchase #4 $64.50   3.399%   $66.6924   $66.69   $66.70   $66.70  
  Purchase #5 $76.51   13.636%   $86.9429   $86.94   $86.95   $86.90  
  Purchase #6 $201.91   4.423%   $210.8405   $210.84   $210.85   $210.80  
  Purchase #7 $158.42   6.424%   $168.5969   $168.60   $168.60   $168.60  
  7 purchase totals = $690.03       $735.3648   $735.36   $735.40   $735.30