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 $229.72   10.867%   $254.6837   $254.68   $254.70   $254.70  
  Purchase #2 $126.53   5.333%   $133.2778   $133.28   $133.30   $133.30  
  Purchase #3 $88.87   13.854%   $101.182   $101.18   $101.20   $101.20  
  Purchase #4 $213.83   3.493%   $221.2991   $221.30   $221.30   $221.30  
  Purchase #5 $189.93   7.696%   $204.547   $204.55   $204.55   $204.50  
  Purchase #6 $199.80   6.843%   $213.4723   $213.47   $213.45   $213.50  
  Purchase #7 $148.60   12.243%   $166.7931   $166.79   $166.80   $166.80  
  7 purchase totals = $1,197.28       $1,295.2550   $1,295.25   $1,295.30   $1,295.30