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 $238.70   12.127%   $267.6471   $267.65   $267.65   $267.60  
  Purchase #2 $158.41   8.289%   $171.5406   $171.54   $171.55   $171.50  
  Purchase #3 $20.50   8.339%   $22.2095   $22.21   $22.20   $22.20  
  Purchase #4 $145.91   13.591%   $165.7406   $165.74   $165.75   $165.70  
  Purchase #5 $76.71   8.453%   $83.1943   $83.19   $83.20   $83.20  
  Purchase #6 $229.97   12.733%   $259.2521   $259.25   $259.25   $259.30  
  Purchase #7 $156.78   9.604%   $171.8372   $171.84   $171.85   $171.80  
  7 purchase totals = $1,026.98       $1,141.4214   $1,141.42   $1,141.45   $1,141.30