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 $93.90   8.134%   $101.5378   $101.54   $101.55   $101.50  
  Purchase #2 $232.83   12.552%   $262.0548   $262.05   $262.05   $262.10  
  Purchase #3 $234.82   7.730%   $252.9716   $252.97   $252.95   $253.00  
  Purchase #4 $86.30   11.842%   $96.5196   $96.52   $96.50   $96.50  
  Purchase #5 $52.38   7.513%   $56.3153   $56.32   $56.30   $56.30  
  Purchase #6 $56.80   3.420%   $58.7426   $58.74   $58.75   $58.70  
  Purchase #7 $187.81   8.302%   $203.402   $203.40   $203.40   $203.40  
  7 purchase totals = $944.84       $1,031.5437   $1,031.54   $1,031.50   $1,031.50