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 $208.29   8.183%   $225.3344   $225.33   $225.35   $225.30  
  Purchase #2 $169.39   8.418%   $183.6493   $183.65   $183.65   $183.60  
  Purchase #3 $14.54   5.381%   $15.3224   $15.32   $15.30   $15.30  
  Purchase #4 $230.32   3.661%   $238.752   $238.75   $238.75   $238.80  
  Purchase #5 $188.79   4.514%   $197.312   $197.31   $197.30   $197.30  
  Purchase #6 $220.83   9.868%   $242.6215   $242.62   $242.60   $242.60  
  Purchase #7 $38.69   5.674%   $40.8853   $40.89   $40.90   $40.90  
  7 purchase totals = $1,070.85       $1,143.8769   $1,143.87   $1,143.85   $1,143.80