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 $46.85   5.278%   $49.3227   $49.32   $49.30   $49.30  
  Purchase #2 $63.36   4.163%   $65.9977   $66.00   $66.00   $66.00  
  Purchase #3 $182.52   8.317%   $197.7002   $197.70   $197.70   $197.70  
  Purchase #4 $114.39   4.501%   $119.5387   $119.54   $119.55   $119.50  
  Purchase #5 $250.25   11.694%   $279.5142   $279.51   $279.50   $279.50  
  Purchase #6 $11.59   6.858%   $12.3848   $12.38   $12.40   $12.40  
  Purchase #7 $118.74   4.453%   $124.0275   $124.03   $124.05   $124.00  
  7 purchase totals = $787.70       $848.4858   $848.48   $848.50   $848.40