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 $187.27   6.726%   $199.8658   $199.87   $199.85   $199.90  
  Purchase #2 $57.81   12.362%   $64.9565   $64.96   $64.95   $65.00  
  Purchase #3 $94.62   3.203%   $97.6507   $97.65   $97.65   $97.70  
  Purchase #4 $177.37   12.220%   $199.0446   $199.04   $199.05   $199.00  
  Purchase #5 $68.33   5.427%   $72.0383   $72.04   $72.05   $72.00  
  Purchase #6 $95.82   9.258%   $104.691   $104.69   $104.70   $104.70  
  Purchase #7 $43.52   10.274%   $47.9912   $47.99   $48.00   $48.00  
  7 purchase totals = $724.74       $786.2381   $786.24   $786.25   $786.30