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 $70.47   8.197%   $76.2464   $76.25   $76.25   $76.20  
  Purchase #2 $202.52   6.568%   $215.8215   $215.82   $215.80   $215.80  
  Purchase #3 $199.60   12.270%   $224.0909   $224.09   $224.10   $224.10  
  Purchase #4 $34.96   7.743%   $37.667   $37.67   $37.65   $37.70  
  Purchase #5 $137.78   7.458%   $148.0556   $148.06   $148.05   $148.10  
  Purchase #6 $174.64   13.105%   $197.5266   $197.53   $197.55   $197.50  
  Purchase #7 $24.29   5.433%   $25.6097   $25.61   $25.60   $25.60  
  7 purchase totals = $844.26       $925.0177   $925.03   $925.00   $925.00