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 $168.83   13.652%   $191.8787   $191.88   $191.90   $191.90  
  Purchase #2 $14.75   10.473%   $16.2948   $16.29   $16.30   $16.30  
  Purchase #3 $45.42   9.185%   $49.5918   $49.59   $49.60   $49.60  
  Purchase #4 $140.84   7.168%   $150.9354   $150.94   $150.95   $150.90  
  Purchase #5 $23.63   10.363%   $26.0788   $26.08   $26.10   $26.10  
  Purchase #6 $209.83   10.865%   $232.628   $232.63   $232.65   $232.60  
  Purchase #7 $89.98   7.829%   $97.0245   $97.02   $97.00   $97.00  
  7 purchase totals = $693.28       $764.4320   $764.43   $764.50   $764.40