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 $223.32   10.304%   $246.3309   $246.33   $246.35   $246.30  
  Purchase #2 $176.75   11.794%   $197.5959   $197.60   $197.60   $197.60  
  Purchase #3 $118.38   3.429%   $122.4393   $122.44   $122.45   $122.40  
  Purchase #4 $189.64   13.844%   $215.8938   $215.89   $215.90   $215.90  
  Purchase #5 $54.43   3.494%   $56.3318   $56.33   $56.35   $56.30  
  Purchase #6 $164.31   7.478%   $176.5971   $176.60   $176.60   $176.60  
  Purchase #7 $193.90   11.305%   $215.8204   $215.82   $215.80   $215.80  
  7 purchase totals = $1,120.73       $1,231.0092   $1,231.01   $1,231.05   $1,230.90