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 $48.51   11.331%   $54.0067   $54.01   $54.00   $54.00  
  Purchase #2 $185.72   9.348%   $203.0811   $203.08   $203.10   $203.10  
  Purchase #3 $221.35   9.176%   $241.6611   $241.66   $241.65   $241.70  
  Purchase #4 $47.71   3.148%   $49.2119   $49.21   $49.20   $49.20  
  Purchase #5 $40.25   13.393%   $45.6407   $45.64   $45.65   $45.60  
  Purchase #6 $157.64   3.246%   $162.757   $162.76   $162.75   $162.80  
  Purchase #7 $45.54   4.293%   $47.495   $47.50   $47.50   $47.50  
  7 purchase totals = $746.72       $803.8535   $803.86   $803.85   $803.90