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 $185.75   4.744%   $194.562   $194.56   $194.55   $194.60  
  Purchase #2 $54.55   3.419%   $56.4151   $56.42   $56.40   $56.40  
  Purchase #3 $16.66   12.120%   $18.6792   $18.68   $18.70   $18.70  
  Purchase #4 $108.71   11.813%   $121.5519   $121.55   $121.55   $121.60  
  Purchase #5 $234.52   13.381%   $265.9011   $265.90   $265.90   $265.90  
  Purchase #6 $247.59   11.197%   $275.3127   $275.31   $275.30   $275.30  
  Purchase #7 $27.55   10.706%   $30.4995   $30.50   $30.50   $30.50  
  7 purchase totals = $875.33       $962.9215   $962.92   $962.90   $963.00