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 $52.92   5.736%   $55.9555   $55.96   $55.95   $56.00  
  Purchase #2 $149.54   3.816%   $155.2464   $155.25   $155.25   $155.20  
  Purchase #3 $139.91   3.216%   $144.4095   $144.41   $144.40   $144.40  
  Purchase #4 $241.89   10.690%   $267.748   $267.75   $267.75   $267.70  
  Purchase #5 $136.46   5.819%   $144.4006   $144.40   $144.40   $144.40  
  Purchase #6 $175.76   12.339%   $197.447   $197.45   $197.45   $197.40  
  Purchase #7 $100.61   8.302%   $108.9626   $108.96   $108.95   $109.00  
  7 purchase totals = $997.09       $1,074.1696   $1,074.18   $1,074.15   $1,074.10