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 $94.62   4.123%   $98.5212   $98.52   $98.50   $98.50  
  Purchase #2 $5.43   13.263%   $6.1502   $6.15   $6.15   $6.20  
  Purchase #3 $196.70   4.486%   $205.524   $205.52   $205.50   $205.50  
  Purchase #4 $172.64   3.247%   $178.2456   $178.25   $178.25   $178.20  
  Purchase #5 $199.98   9.785%   $219.548   $219.55   $219.55   $219.50  
  Purchase #6 $71.90   3.434%   $74.369   $74.37   $74.35   $74.40  
  Purchase #7 $33.97   5.392%   $35.8017   $35.80   $35.80   $35.80  
  7 purchase totals = $775.24       $818.1597   $818.16   $818.10   $818.10