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 $40.82   5.802%   $43.1884   $43.19   $43.20   $43.20  
  Purchase #2 $221.26   10.663%   $244.853   $244.85   $244.85   $244.90  
  Purchase #3 $58.31   11.484%   $65.0063   $65.01   $65.00   $65.00  
  Purchase #4 $47.32   13.435%   $53.6774   $53.68   $53.70   $53.70  
  Purchase #5 $154.68   6.268%   $164.3753   $164.38   $164.40   $164.40  
  Purchase #6 $151.82   5.424%   $160.0547   $160.05   $160.05   $160.10  
  Purchase #7 $206.66   6.261%   $219.599   $219.60   $219.60   $219.60  
  7 purchase totals = $880.87       $950.7541   $950.76   $950.80   $950.90