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 $140.66   4.700%   $147.271   $147.27   $147.25   $147.30  
  Purchase #2 $6.80   13.232%   $7.6998   $7.70   $7.70   $7.70  
  Purchase #3 $76.89   5.346%   $81.0005   $81.00   $81.00   $81.00  
  Purchase #4 $121.62   6.872%   $129.9777   $129.98   $130.00   $130.00  
  Purchase #5 $24.93   13.590%   $28.318   $28.32   $28.30   $28.30  
  Purchase #6 $128.85   5.682%   $136.1713   $136.17   $136.15   $136.20  
  Purchase #7 $90.81   3.443%   $93.9366   $93.94   $93.95   $93.90  
  7 purchase totals = $590.56       $624.3749   $624.38   $624.35   $624.40