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 $113.27   8.756%   $123.1879   $123.19   $123.20   $123.20  
  Purchase #2 $145.90   13.236%   $165.2113   $165.21   $165.20   $165.20  
  Purchase #3 $159.75   4.686%   $167.2359   $167.24   $167.25   $167.20  
  Purchase #4 $23.85   3.107%   $24.591   $24.59   $24.60   $24.60  
  Purchase #5 $93.51   12.108%   $104.8322   $104.83   $104.85   $104.80  
  Purchase #6 $212.70   9.314%   $232.5109   $232.51   $232.50   $232.50  
  Purchase #7 $122.92   7.795%   $132.5016   $132.50   $132.50   $132.50  
  7 purchase totals = $871.90       $950.0708   $950.07   $950.10   $950.00