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 $69.65   6.674%   $74.2984   $74.30   $74.30   $74.30  
  Purchase #2 $190.51   11.443%   $212.3101   $212.31   $212.30   $212.30  
  Purchase #3 $238.79   3.230%   $246.5029   $246.50   $246.50   $246.50  
  Purchase #4 $245.73   12.349%   $276.0752   $276.08   $276.10   $276.10  
  Purchase #5 $218.87   13.773%   $249.015   $249.02   $249.00   $249.00  
  Purchase #6 $224.74   13.677%   $255.4777   $255.48   $255.50   $255.50  
  Purchase #7 $18.32   11.802%   $20.4821   $20.48   $20.50   $20.50  
  7 purchase totals = $1,206.61       $1,334.1614   $1,334.17   $1,334.20   $1,334.20