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 $188.31   8.705%   $204.7024   $204.70   $204.70   $204.70  
  Purchase #2 $107.82   10.631%   $119.2823   $119.28   $119.30   $119.30  
  Purchase #3 $46.44   12.266%   $52.1363   $52.14   $52.15   $52.10  
  Purchase #4 $139.51   3.243%   $144.0343   $144.03   $144.05   $144.00  
  Purchase #5 $176.50   11.731%   $197.2052   $197.21   $197.20   $197.20  
  Purchase #6 $144.93   4.149%   $150.9431   $150.94   $150.95   $150.90  
  Purchase #7 $38.43   4.290%   $40.0786   $40.08   $40.10   $40.10  
  7 purchase totals = $841.94       $908.3822   $908.38   $908.45   $908.30