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 $33.66   5.562%   $35.5322   $35.53   $35.55   $35.50  
  Purchase #2 $207.81   8.744%   $225.9809   $225.98   $226.00   $226.00  
  Purchase #3 $16.34   8.626%   $17.7495   $17.75   $17.75   $17.70  
  Purchase #4 $157.43   5.372%   $165.8871   $165.89   $165.90   $165.90  
  Purchase #5 $247.40   3.387%   $255.7794   $255.78   $255.80   $255.80  
  Purchase #6 $19.64   11.375%   $21.8741   $21.87   $21.85   $21.90  
  Purchase #7 $249.80   9.434%   $273.3661   $273.37   $273.35   $273.40  
  7 purchase totals = $932.08       $996.1693   $996.17   $996.20   $996.20