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 $118.40   6.209%   $125.7515   $125.75   $125.75   $125.80  
  Purchase #2 $233.51   5.336%   $245.9701   $245.97   $245.95   $246.00  
  Purchase #3 $72.63   4.852%   $76.154   $76.15   $76.15   $76.20  
  Purchase #4 $243.51   10.759%   $269.7092   $269.71   $269.70   $269.70  
  Purchase #5 $190.35   7.761%   $205.1231   $205.12   $205.10   $205.10  
  Purchase #6 $86.84   6.305%   $92.3153   $92.32   $92.30   $92.30  
  Purchase #7 $22.80   11.305%   $25.3775   $25.38   $25.40   $25.40  
  7 purchase totals = $968.04       $1,040.4007   $1,040.40   $1,040.35   $1,040.50