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 $55.31   5.677%   $58.4499   $58.45   $58.45   $58.40  
  Purchase #2 $192.72   5.193%   $202.7279   $202.73   $202.75   $202.70  
  Purchase #3 $202.51   11.862%   $226.5317   $226.53   $226.55   $226.50  
  Purchase #4 $207.86   6.363%   $221.0861   $221.09   $221.10   $221.10  
  Purchase #5 $90.45   3.559%   $93.6691   $93.67   $93.65   $93.70  
  Purchase #6 $124.44   5.674%   $131.5007   $131.50   $131.50   $131.50  
  Purchase #7 $75.50   11.765%   $84.3826   $84.38   $84.40   $84.40  
  7 purchase totals = $948.79       $1,018.3480   $1,018.35   $1,018.40   $1,018.30