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 $231.59   4.619%   $242.2871   $242.29   $242.30   $242.30  
  Purchase #2 $71.63   5.647%   $75.6749   $75.67   $75.65   $75.70  
  Purchase #3 $227.69   3.633%   $235.962   $235.96   $235.95   $236.00  
  Purchase #4 $206.33   13.687%   $234.5704   $234.57   $234.55   $234.60  
  Purchase #5 $104.80   8.470%   $113.6766   $113.68   $113.70   $113.70  
  Purchase #6 $205.67   3.863%   $213.615   $213.62   $213.60   $213.60  
  Purchase #7 $229.78   10.222%   $253.2681   $253.27   $253.25   $253.30  
  7 purchase totals = $1,277.49       $1,369.0541   $1,369.06   $1,369.00   $1,369.20