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 $201.69   11.560%   $225.0054   $225.01   $225.00   $225.00  
  Purchase #2 $159.93   9.114%   $174.506   $174.51   $174.50   $174.50  
  Purchase #3 $244.87   9.410%   $267.9123   $267.91   $267.90   $267.90  
  Purchase #4 $47.44   7.119%   $50.8173   $50.82   $50.80   $50.80  
  Purchase #5 $42.33   3.848%   $43.9589   $43.96   $43.95   $44.00  
  Purchase #6 $53.74   12.643%   $60.5343   $60.53   $60.55   $60.50  
  Purchase #7 $27.65   3.593%   $28.6435   $28.64   $28.65   $28.60  
  7 purchase totals = $777.65       $851.3777   $851.38   $851.35   $851.30