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 $87.86   9.348%   $96.0732   $96.07   $96.05   $96.10  
  Purchase #2 $232.92   8.652%   $253.0722   $253.07   $253.05   $253.10  
  Purchase #3 $30.31   3.272%   $31.3017   $31.30   $31.30   $31.30  
  Purchase #4 $55.70   9.421%   $60.9475   $60.95   $60.95   $60.90  
  Purchase #5 $216.99   4.181%   $226.0624   $226.06   $226.05   $226.10  
  Purchase #6 $62.66   3.701%   $64.979   $64.98   $65.00   $65.00  
  Purchase #7 $182.68   6.622%   $194.7771   $194.78   $194.80   $194.80  
  7 purchase totals = $869.12       $927.2131   $927.21   $927.20   $927.30