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 $86.30   12.202%   $96.8303   $96.83   $96.85   $96.80  
  Purchase #2 $166.98   10.216%   $184.0387   $184.04   $184.05   $184.00  
  Purchase #3 $101.32   11.817%   $113.293   $113.29   $113.30   $113.30  
  Purchase #4 $188.81   7.369%   $202.7234   $202.72   $202.70   $202.70  
  Purchase #5 $97.71   8.159%   $105.6822   $105.68   $105.70   $105.70  
  Purchase #6 $137.76   13.466%   $156.3108   $156.31   $156.30   $156.30  
  Purchase #7 $98.52   6.870%   $105.2883   $105.29   $105.30   $105.30  
  7 purchase totals = $877.40       $964.1667   $964.16   $964.20   $964.10