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 $86.94   11.805%   $97.2033   $97.20   $97.20   $97.20  
  Purchase #2 $164.45   13.489%   $186.6327   $186.63   $186.65   $186.60  
  Purchase #3 $164.65   5.475%   $173.6646   $173.66   $173.65   $173.70  
  Purchase #4 $89.52   10.205%   $98.6555   $98.66   $98.65   $98.70  
  Purchase #5 $25.56   5.557%   $26.9804   $26.98   $27.00   $27.00  
  Purchase #6 $222.38   13.515%   $252.4347   $252.43   $252.45   $252.40  
  Purchase #7 $202.90   5.558%   $214.1772   $214.18   $214.20   $214.20  
  7 purchase totals = $956.40       $1,049.7484   $1,049.74   $1,049.80   $1,049.80