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 $89.80   5.509%   $94.7471   $94.75   $94.75   $94.70  
  Purchase #2 $64.27   12.551%   $72.3365   $72.34   $72.35   $72.30  
  Purchase #3 $151.84   7.873%   $163.7944   $163.79   $163.80   $163.80  
  Purchase #4 $206.56   12.152%   $231.6612   $231.66   $231.65   $231.70  
  Purchase #5 $230.72   6.190%   $245.0016   $245.00   $245.00   $245.00  
  Purchase #6 $179.47   12.524%   $201.9468   $201.95   $201.95   $201.90  
  Purchase #7 $234.61   11.305%   $261.1327   $261.13   $261.15   $261.10  
  7 purchase totals = $1,157.27       $1,270.6203   $1,270.62   $1,270.65   $1,270.50