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 $116.84   6.359%   $124.2699   $124.27   $124.25   $124.30  
  Purchase #2 $196.66   13.675%   $223.5533   $223.55   $223.55   $223.60  
  Purchase #3 $157.97   7.323%   $169.5381   $169.54   $169.55   $169.50  
  Purchase #4 $216.75   3.416%   $224.1542   $224.15   $224.15   $224.20  
  Purchase #5 $191.89   7.291%   $205.8807   $205.88   $205.90   $205.90  
  Purchase #6 $97.67   13.629%   $110.9814   $110.98   $111.00   $111.00  
  Purchase #7 $181.44   12.678%   $204.443   $204.44   $204.45   $204.40  
  7 purchase totals = $1,159.22       $1,262.8206   $1,262.81   $1,262.85   $1,262.90