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 $234.36   5.432%   $247.0904   $247.09   $247.10   $247.10  
  Purchase #2 $115.70   9.201%   $126.3456   $126.35   $126.35   $126.30  
  Purchase #3 $110.96   4.725%   $116.2029   $116.20   $116.20   $116.20  
  Purchase #4 $143.99   13.172%   $162.9564   $162.96   $162.95   $163.00  
  Purchase #5 $159.63   6.425%   $169.8862   $169.89   $169.90   $169.90  
  Purchase #6 $181.37   13.382%   $205.6409   $205.64   $205.65   $205.60  
  Purchase #7 $207.50   6.130%   $220.2198   $220.22   $220.20   $220.20  
  7 purchase totals = $1,153.51       $1,248.3422   $1,248.35   $1,248.35   $1,248.30