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 $215.71   9.494%   $236.1895   $236.19   $236.20   $236.20  
  Purchase #2 $86.29   8.167%   $93.3373   $93.34   $93.35   $93.30  
  Purchase #3 $87.48   8.364%   $94.7968   $94.80   $94.80   $94.80  
  Purchase #4 $45.67   8.127%   $49.3816   $49.38   $49.40   $49.40  
  Purchase #5 $244.72   13.297%   $277.2604   $277.26   $277.25   $277.30  
  Purchase #6 $163.32   12.254%   $183.3332   $183.33   $183.35   $183.30  
  Purchase #7 $61.81   12.848%   $69.7513   $69.75   $69.75   $69.80  
  7 purchase totals = $905.00       $1,004.0501   $1,004.05   $1,004.10   $1,004.10