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 $162.84   9.178%   $177.7855   $177.79   $177.80   $177.80  
  Purchase #2 $223.90   4.570%   $234.1322   $234.13   $234.15   $234.10  
  Purchase #3 $123.40   10.606%   $136.4878   $136.49   $136.50   $136.50  
  Purchase #4 $182.28   3.547%   $188.7455   $188.75   $188.75   $188.70  
  Purchase #5 $84.66   13.351%   $95.963   $95.96   $95.95   $96.00  
  Purchase #6 $195.97   8.459%   $212.5471   $212.55   $212.55   $212.50  
  Purchase #7 $173.38   9.683%   $190.1684   $190.17   $190.15   $190.20  
  7 purchase totals = $1,146.43       $1,235.8295   $1,235.84   $1,235.85   $1,235.80