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 $106.93   11.264%   $118.9746   $118.97   $118.95   $119.00  
  Purchase #2 $39.37   5.494%   $41.533   $41.53   $41.55   $41.50  
  Purchase #3 $109.63   5.289%   $115.4283   $115.43   $115.45   $115.40  
  Purchase #4 $196.86   8.848%   $214.2782   $214.28   $214.30   $214.30  
  Purchase #5 $116.91   7.171%   $125.2936   $125.29   $125.30   $125.30  
  Purchase #6 $245.52   6.644%   $261.8323   $261.83   $261.85   $261.80  
  Purchase #7 $224.26   7.373%   $240.7947   $240.79   $240.80   $240.80  
  7 purchase totals = $1,039.48       $1,118.1347   $1,118.12   $1,118.20   $1,118.10