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 $83.98   11.610%   $93.7301   $93.73   $93.75   $93.70  
  Purchase #2 $92.92   3.373%   $96.0542   $96.05   $96.05   $96.10  
  Purchase #3 $45.84   9.639%   $50.2585   $50.26   $50.25   $50.30  
  Purchase #4 $203.69   4.146%   $212.135   $212.14   $212.15   $212.10  
  Purchase #5 $28.50   4.217%   $29.7018   $29.70   $29.70   $29.70  
  Purchase #6 $154.62   7.659%   $166.4623   $166.46   $166.45   $166.50  
  Purchase #7 $165.79   7.560%   $178.3237   $178.32   $178.30   $178.30  
  7 purchase totals = $775.34       $826.6656   $826.66   $826.65   $826.70