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 $208.62   12.522%   $234.7434   $234.74   $234.75   $234.70  
  Purchase #2 $61.42   4.652%   $64.2773   $64.28   $64.30   $64.30  
  Purchase #3 $24.30   6.734%   $25.9364   $25.94   $25.95   $25.90  
  Purchase #4 $88.90   5.236%   $93.5548   $93.55   $93.55   $93.60  
  Purchase #5 $189.41   8.241%   $205.0193   $205.02   $205.00   $205.00  
  Purchase #6 $13.55   5.408%   $14.2828   $14.28   $14.30   $14.30  
  Purchase #7 $51.65   13.156%   $58.4451   $58.45   $58.45   $58.40  
  7 purchase totals = $637.85       $696.2591   $696.26   $696.30   $696.20