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 $117.52   6.337%   $124.9672   $124.97   $124.95   $125.00  
  Purchase #2 $210.81   9.523%   $230.8854   $230.89   $230.90   $230.90  
  Purchase #3 $61.94   3.746%   $64.2603   $64.26   $64.25   $64.30  
  Purchase #4 $186.84   11.832%   $208.9469   $208.95   $208.95   $208.90  
  Purchase #5 $180.70   4.870%   $189.5001   $189.50   $189.50   $189.50  
  Purchase #6 $94.64   13.726%   $107.6303   $107.63   $107.65   $107.60  
  Purchase #7 $87.66   11.556%   $97.79   $97.79   $97.80   $97.80  
  7 purchase totals = $940.11       $1,023.9802   $1,023.99   $1,024.00   $1,024.00