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 $189.94   12.771%   $214.1972   $214.20   $214.20   $214.20  
  Purchase #2 $75.31   10.226%   $83.0112   $83.01   $83.00   $83.00  
  Purchase #3 $174.92   3.321%   $180.7291   $180.73   $180.75   $180.70  
  Purchase #4 $139.42   11.216%   $155.0573   $155.06   $155.05   $155.10  
  Purchase #5 $67.40   6.202%   $71.5801   $71.58   $71.60   $71.60  
  Purchase #6 $165.77   6.393%   $176.3677   $176.37   $176.35   $176.40  
  Purchase #7 $129.27   9.370%   $141.3826   $141.38   $141.40   $141.40  
  7 purchase totals = $942.03       $1,022.3252   $1,022.33   $1,022.35   $1,022.40