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 $245.30   8.831%   $266.9624   $266.96   $266.95   $267.00  
  Purchase #2 $57.26   5.408%   $60.3566   $60.36   $60.35   $60.40  
  Purchase #3 $198.90   10.507%   $219.7984   $219.80   $219.80   $219.80  
  Purchase #4 $151.98   4.304%   $158.5212   $158.52   $158.50   $158.50  
  Purchase #5 $190.27   4.576%   $198.9768   $198.98   $199.00   $199.00  
  Purchase #6 $154.63   3.425%   $159.9261   $159.93   $159.95   $159.90  
  Purchase #7 $84.32   5.130%   $88.6456   $88.65   $88.65   $88.60  
  7 purchase totals = $1,082.66       $1,153.1871   $1,153.20   $1,153.20   $1,153.20