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 $211.49   5.773%   $223.6993   $223.70   $223.70   $223.70  
  Purchase #2 $8.26   13.303%   $9.3588   $9.36   $9.35   $9.40  
  Purchase #3 $58.68   6.703%   $62.6133   $62.61   $62.60   $62.60  
  Purchase #4 $124.39   6.173%   $132.0686   $132.07   $132.05   $132.10  
  Purchase #5 $9.51   10.641%   $10.522   $10.52   $10.50   $10.50  
  Purchase #6 $23.73   10.762%   $26.2838   $26.28   $26.30   $26.30  
  Purchase #7 $7.36   12.124%   $8.2523   $8.25   $8.25   $8.30  
  7 purchase totals = $443.42       $472.7981   $472.79   $472.75   $472.90