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 $248.44   7.554%   $267.2072   $267.21   $267.20   $267.20  
  Purchase #2 $144.53   4.273%   $150.7058   $150.71   $150.70   $150.70  
  Purchase #3 $117.47   11.445%   $130.9144   $130.91   $130.90   $130.90  
  Purchase #4 $47.88   8.192%   $51.8023   $51.80   $51.80   $51.80  
  Purchase #5 $29.93   9.437%   $32.7545   $32.75   $32.75   $32.80  
  Purchase #6 $97.35   6.335%   $103.5171   $103.52   $103.50   $103.50  
  Purchase #7 $138.90   5.864%   $147.0451   $147.05   $147.05   $147.00  
  7 purchase totals = $824.50       $883.9464   $883.95   $883.90   $883.90