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 $153.97   7.754%   $165.9088   $165.91   $165.90   $165.90  
  Purchase #2 $23.93   6.293%   $25.4359   $25.44   $25.45   $25.40  
  Purchase #3 $165.95   11.299%   $184.7007   $184.70   $184.70   $184.70  
  Purchase #4 $116.32   13.650%   $132.1977   $132.20   $132.20   $132.20  
  Purchase #5 $208.53   3.817%   $216.4896   $216.49   $216.50   $216.50  
  Purchase #6 $119.61   7.743%   $128.8714   $128.87   $128.85   $128.90  
  Purchase #7 $88.74   4.338%   $92.5895   $92.59   $92.60   $92.60  
  7 purchase totals = $877.05       $946.1936   $946.20   $946.20   $946.20