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 $9.30   7.160%   $9.9659   $9.97   $9.95   $10.00  
  Purchase #2 $117.49   6.501%   $125.128   $125.13   $125.15   $125.10  
  Purchase #3 $42.81   6.369%   $45.5366   $45.54   $45.55   $45.50  
  Purchase #4 $71.83   9.699%   $78.7968   $78.80   $78.80   $78.80  
  Purchase #5 $235.32   5.401%   $248.0296   $248.03   $248.05   $248.00  
  Purchase #6 $64.69   7.210%   $69.3541   $69.35   $69.35   $69.40  
  Purchase #7 $227.35   8.756%   $247.2568   $247.26   $247.25   $247.30  
  7 purchase totals = $768.79       $824.0678   $824.08   $824.10   $824.10