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 $56.53   13.238%   $64.0134   $64.01   $64.00   $64.00  
  Purchase #2 $117.88   8.725%   $128.165   $128.17   $128.15   $128.20  
  Purchase #3 $232.58   3.809%   $241.439   $241.44   $241.45   $241.40  
  Purchase #4 $191.60   11.298%   $213.247   $213.25   $213.25   $213.20  
  Purchase #5 $156.46   4.189%   $163.0141   $163.01   $163.00   $163.00  
  Purchase #6 $162.64   11.306%   $181.0281   $181.03   $181.05   $181.00  
  Purchase #7 $40.25   8.416%   $43.6374   $43.64   $43.65   $43.60  
  7 purchase totals = $957.94       $1,034.5440   $1,034.55   $1,034.55   $1,034.40