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 $68.33   8.786%   $74.3335   $74.33   $74.35   $74.30  
  Purchase #2 $193.77   8.349%   $209.9479   $209.95   $209.95   $209.90  
  Purchase #3 $100.95   11.372%   $112.43   $112.43   $112.45   $112.40  
  Purchase #4 $158.81   4.256%   $165.569   $165.57   $165.55   $165.60  
  Purchase #5 $225.70   3.816%   $234.3127   $234.31   $234.30   $234.30  
  Purchase #6 $5.48   4.480%   $5.7255   $5.73   $5.75   $5.70  
  Purchase #7 $116.79   10.619%   $129.1919   $129.19   $129.20   $129.20  
  7 purchase totals = $869.83       $931.5105   $931.51   $931.55   $931.40