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 $244.97   12.398%   $275.3414   $275.34   $275.35   $275.30  
  Purchase #2 $118.51   11.124%   $131.6931   $131.69   $131.70   $131.70  
  Purchase #3 $207.32   4.278%   $216.1891   $216.19   $216.20   $216.20  
  Purchase #4 $234.52   11.590%   $261.7009   $261.70   $261.70   $261.70  
  Purchase #5 $179.71   12.123%   $201.4962   $201.50   $201.50   $201.50  
  Purchase #6 $232.26   5.497%   $245.0273   $245.03   $245.05   $245.00  
  Purchase #7 $97.66   7.530%   $105.0138   $105.01   $105.00   $105.00  
  7 purchase totals = $1,314.95       $1,436.4618   $1,436.46   $1,436.50   $1,436.40