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 $236.86   12.822%   $267.2302   $267.23   $267.25   $267.20  
  Purchase #2 $24.47   3.326%   $25.2839   $25.28   $25.30   $25.30  
  Purchase #3 $94.35   3.404%   $97.5617   $97.56   $97.55   $97.60  
  Purchase #4 $184.63   13.294%   $209.1747   $209.17   $209.15   $209.20  
  Purchase #5 $170.38   13.209%   $192.8855   $192.89   $192.90   $192.90  
  Purchase #6 $112.55   6.116%   $119.4336   $119.43   $119.45   $119.40  
  Purchase #7 $141.39   7.869%   $152.516   $152.52   $152.50   $152.50  
  7 purchase totals = $964.63       $1,064.0856   $1,064.08   $1,064.10   $1,064.10