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 $61.67   10.774%   $68.3143   $68.31   $68.30   $68.30  
  Purchase #2 $111.37   12.446%   $125.2311   $125.23   $125.25   $125.20  
  Purchase #3 $144.97   7.865%   $156.3719   $156.37   $156.35   $156.40  
  Purchase #4 $24.75   9.412%   $27.0795   $27.08   $27.10   $27.10  
  Purchase #5 $236.90   8.396%   $256.7901   $256.79   $256.80   $256.80  
  Purchase #6 $238.62   9.386%   $261.0169   $261.02   $261.00   $261.00  
  Purchase #7 $13.84   6.510%   $14.741   $14.74   $14.75   $14.70  
  7 purchase totals = $832.12       $909.5448   $909.54   $909.55   $909.50