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 $23.46   6.731%   $25.0391   $25.04   $25.05   $25.00  
  Purchase #2 $250.70   4.481%   $261.9339   $261.93   $261.95   $261.90  
  Purchase #3 $55.75   12.845%   $62.9111   $62.91   $62.90   $62.90  
  Purchase #4 $223.81   7.370%   $240.3048   $240.30   $240.30   $240.30  
  Purchase #5 $194.66   3.813%   $202.0824   $202.08   $202.10   $202.10  
  Purchase #6 $48.40   8.531%   $52.529   $52.53   $52.55   $52.50  
  Purchase #7 $11.98   12.732%   $13.5053   $13.51   $13.50   $13.50  
  7 purchase totals = $808.76       $858.3056   $858.30   $858.35   $858.20