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 $42.52   5.243%   $44.7493   $44.75   $44.75   $44.70  
  Purchase #2 $223.76   5.171%   $235.3306   $235.33   $235.35   $235.30  
  Purchase #3 $82.75   11.773%   $92.4922   $92.49   $92.50   $92.50  
  Purchase #4 $55.39   12.652%   $62.3979   $62.40   $62.40   $62.40  
  Purchase #5 $114.28   9.369%   $124.9869   $124.99   $125.00   $125.00  
  Purchase #6 $57.52   13.820%   $65.4693   $65.47   $65.45   $65.50  
  Purchase #7 $130.71   7.722%   $140.8034   $140.80   $140.80   $140.80  
  7 purchase totals = $706.93       $766.2296   $766.23   $766.25   $766.20