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 $95.67   6.313%   $101.7096   $101.71   $101.70   $101.70  
  Purchase #2 $224.95   9.322%   $245.9198   $245.92   $245.90   $245.90  
  Purchase #3 $197.52   5.657%   $208.6937   $208.69   $208.70   $208.70  
  Purchase #4 $169.27   4.125%   $176.2524   $176.25   $176.25   $176.30  
  Purchase #5 $54.73   13.700%   $62.228   $62.23   $62.25   $62.20  
  Purchase #6 $116.70   10.168%   $128.5661   $128.57   $128.55   $128.60  
  Purchase #7 $156.64   8.156%   $169.4156   $169.42   $169.40   $169.40  
  7 purchase totals = $1,015.48       $1,092.7852   $1,092.79   $1,092.75   $1,092.80