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 $248.98   13.865%   $283.5011   $283.50   $283.50   $283.50  
  Purchase #2 $85.28   5.588%   $90.0454   $90.05   $90.05   $90.00  
  Purchase #3 $96.39   4.873%   $101.0871   $101.09   $101.10   $101.10  
  Purchase #4 $84.87   7.731%   $91.4313   $91.43   $91.45   $91.40  
  Purchase #5 $209.47   4.648%   $219.2062   $219.21   $219.20   $219.20  
  Purchase #6 $91.63   7.170%   $98.1999   $98.20   $98.20   $98.20  
  Purchase #7 $54.69   13.348%   $61.99   $61.99   $62.00   $62.00  
  7 purchase totals = $871.31       $945.4610   $945.47   $945.50   $945.40