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 $59.69   10.855%   $66.1693   $66.17   $66.15   $66.20  
  Purchase #2 $224.57   6.528%   $239.2299   $239.23   $239.25   $239.20  
  Purchase #3 $79.49   4.364%   $82.9589   $82.96   $82.95   $83.00  
  Purchase #4 $232.76   10.179%   $256.4526   $256.45   $256.45   $256.50  
  Purchase #5 $219.61   11.788%   $245.4976   $245.50   $245.50   $245.50  
  Purchase #6 $62.28   12.393%   $69.9984   $70.00   $70.00   $70.00  
  Purchase #7 $100.89   5.544%   $106.4833   $106.48   $106.50   $106.50  
  7 purchase totals = $979.29       $1,066.7900   $1,066.79   $1,066.80   $1,066.90