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 $191.55   5.559%   $202.1983   $202.20   $202.20   $202.20  
  Purchase #2 $30.81   6.328%   $32.7597   $32.76   $32.75   $32.80  
  Purchase #3 $180.27   9.682%   $197.7237   $197.72   $197.70   $197.70  
  Purchase #4 $103.39   12.172%   $115.9746   $115.97   $115.95   $116.00  
  Purchase #5 $109.34   12.828%   $123.3661   $123.37   $123.35   $123.40  
  Purchase #6 $54.31   3.607%   $56.269   $56.27   $56.25   $56.30  
  Purchase #7 $165.98   9.833%   $182.3008   $182.30   $182.30   $182.30  
  7 purchase totals = $835.65       $910.5922   $910.59   $910.50   $910.70