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 $139.91   10.738%   $154.9335   $154.93   $154.95   $154.90  
  Purchase #2 $72.87   12.132%   $81.7106   $81.71   $81.70   $81.70  
  Purchase #3 $221.79   12.420%   $249.3363   $249.34   $249.35   $249.30  
  Purchase #4 $167.87   6.676%   $179.077   $179.08   $179.10   $179.10  
  Purchase #5 $12.79   12.356%   $14.3703   $14.37   $14.35   $14.40  
  Purchase #6 $91.43   12.250%   $102.6302   $102.63   $102.65   $102.60  
  Purchase #7 $217.76   6.688%   $232.3238   $232.32   $232.30   $232.30  
  7 purchase totals = $924.42       $1,014.3817   $1,014.38   $1,014.40   $1,014.30