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 $204.26   6.218%   $216.9609   $216.96   $216.95   $217.00  
  Purchase #2 $80.65   12.633%   $90.8385   $90.84   $90.85   $90.80  
  Purchase #3 $109.72   4.604%   $114.7715   $114.77   $114.75   $114.80  
  Purchase #4 $109.76   13.130%   $124.1715   $124.17   $124.15   $124.20  
  Purchase #5 $193.29   6.340%   $205.5446   $205.54   $205.55   $205.50  
  Purchase #6 $55.63   4.843%   $58.3242   $58.32   $58.30   $58.30  
  Purchase #7 $173.68   12.688%   $195.7165   $195.72   $195.70   $195.70  
  7 purchase totals = $926.99       $1,006.3277   $1,006.32   $1,006.25   $1,006.30