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 $179.70   8.662%   $195.2656   $195.27   $195.25   $195.30  
  Purchase #2 $33.71   10.735%   $37.3288   $37.33   $37.35   $37.30  
  Purchase #3 $153.64   8.201%   $166.24   $166.24   $166.25   $166.20  
  Purchase #4 $240.79   13.724%   $273.836   $273.84   $273.85   $273.80  
  Purchase #5 $218.83   5.364%   $230.568   $230.57   $230.55   $230.60  
  Purchase #6 $63.47   4.103%   $66.0742   $66.07   $66.05   $66.10  
  Purchase #7 $12.86   13.714%   $14.6236   $14.62   $14.60   $14.60  
  7 purchase totals = $903.00       $983.9362   $983.94   $983.90   $983.90