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 $237.27   3.481%   $245.5294   $245.53   $245.55   $245.50  
  Purchase #2 $236.87   9.184%   $258.6241   $258.62   $258.60   $258.60  
  Purchase #3 $172.57   13.136%   $195.2388   $195.24   $195.25   $195.20  
  Purchase #4 $152.67   5.422%   $160.9478   $160.95   $160.95   $160.90  
  Purchase #5 $230.72   9.297%   $252.17   $252.17   $252.15   $252.20  
  Purchase #6 $163.53   13.415%   $185.4675   $185.47   $185.45   $185.50  
  Purchase #7 $197.96   9.155%   $216.0832   $216.08   $216.10   $216.10  
  7 purchase totals = $1,391.59       $1,514.0608   $1,514.06   $1,514.05   $1,514.00