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 $246.86   8.255%   $267.2383   $267.24   $267.25   $267.20  
  Purchase #2 $57.47   13.127%   $65.0141   $65.01   $65.00   $65.00  
  Purchase #3 $191.72   3.417%   $198.2711   $198.27   $198.25   $198.30  
  Purchase #4 $37.65   9.816%   $41.3457   $41.35   $41.35   $41.30  
  Purchase #5 $136.69   8.785%   $148.6982   $148.70   $148.70   $148.70  
  Purchase #6 $158.54   9.757%   $174.0087   $174.01   $174.00   $174.00  
  Purchase #7 $95.53   4.394%   $99.7276   $99.73   $99.75   $99.70  
  7 purchase totals = $924.46       $994.3037   $994.31   $994.30   $994.20