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 $236.67   7.802%   $255.135   $255.14   $255.15   $255.10  
  Purchase #2 $69.51   5.718%   $73.4846   $73.48   $73.50   $73.50  
  Purchase #3 $199.74   6.149%   $212.022   $212.02   $212.00   $212.00  
  Purchase #4 $108.62   6.692%   $115.8889   $115.89   $115.90   $115.90  
  Purchase #5 $117.62   7.204%   $126.0933   $126.09   $126.10   $126.10  
  Purchase #6 $208.79   10.437%   $230.5814   $230.58   $230.60   $230.60  
  Purchase #7 $109.79   11.117%   $121.9954   $122.00   $122.00   $122.00  
  7 purchase totals = $1,050.74       $1,135.2006   $1,135.20   $1,135.25   $1,135.20