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 $236.62   6.482%   $251.9577   $251.96   $251.95   $252.00  
  Purchase #2 $66.51   13.680%   $75.6086   $75.61   $75.60   $75.60  
  Purchase #3 $72.25   6.163%   $76.7028   $76.70   $76.70   $76.70  
  Purchase #4 $85.28   13.272%   $96.5984   $96.60   $96.60   $96.60  
  Purchase #5 $136.40   6.165%   $144.8091   $144.81   $144.80   $144.80  
  Purchase #6 $144.51   13.318%   $163.7558   $163.76   $163.75   $163.80  
  Purchase #7 $51.92   4.166%   $54.083   $54.08   $54.10   $54.10  
  7 purchase totals = $793.49       $863.5154   $863.52   $863.50   $863.60