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 $71.72   6.109%   $76.1014   $76.10   $76.10   $76.10  
  Purchase #2 $203.66   13.189%   $230.5207   $230.52   $230.50   $230.50  
  Purchase #3 $187.70   9.478%   $205.4902   $205.49   $205.50   $205.50  
  Purchase #4 $32.26   7.439%   $34.6598   $34.66   $34.65   $34.70  
  Purchase #5 $146.58   7.191%   $157.1206   $157.12   $157.10   $157.10  
  Purchase #6 $48.43   10.452%   $53.4919   $53.49   $53.50   $53.50  
  Purchase #7 $8.29   6.775%   $8.8516   $8.85   $8.85   $8.90  
  7 purchase totals = $698.64       $766.2362   $766.23   $766.20   $766.30