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 $59.91   11.291%   $66.6744   $66.67   $66.65   $66.70  
  Purchase #2 $205.39   7.679%   $221.1619   $221.16   $221.15   $221.20  
  Purchase #3 $246.48   11.403%   $274.5861   $274.59   $274.60   $274.60  
  Purchase #4 $200.64   9.270%   $219.2393   $219.24   $219.25   $219.20  
  Purchase #5 $8.42   9.770%   $9.2426   $9.24   $9.25   $9.20  
  Purchase #6 $72.65   3.174%   $74.9559   $74.96   $74.95   $75.00  
  Purchase #7 $216.48   13.783%   $246.3174   $246.32   $246.30   $246.30  
  7 purchase totals = $1,009.97       $1,112.1776   $1,112.18   $1,112.15   $1,112.20