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 $97.73   9.636%   $107.1473   $107.15   $107.15   $107.10  
  Purchase #2 $181.80   8.557%   $197.3566   $197.36   $197.35   $197.40  
  Purchase #3 $158.98   8.433%   $172.3868   $172.39   $172.40   $172.40  
  Purchase #4 $154.94   9.659%   $169.9057   $169.91   $169.90   $169.90  
  Purchase #5 $94.71   4.594%   $99.061   $99.06   $99.05   $99.10  
  Purchase #6 $11.45   13.848%   $13.0356   $13.04   $13.05   $13.00  
  Purchase #7 $185.37   10.358%   $204.5706   $204.57   $204.55   $204.60  
  7 purchase totals = $884.98       $963.4636   $963.48   $963.45   $963.50