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 $86.74   10.633%   $95.9631   $95.96   $95.95   $96.00  
  Purchase #2 $112.86   6.703%   $120.425   $120.43   $120.45   $120.40  
  Purchase #3 $80.61   9.825%   $88.5299   $88.53   $88.55   $88.50  
  Purchase #4 $84.79   8.190%   $91.7343   $91.73   $91.75   $91.70  
  Purchase #5 $73.52   3.434%   $76.0447   $76.04   $76.05   $76.00  
  Purchase #6 $107.82   6.111%   $114.4089   $114.41   $114.40   $114.40  
  Purchase #7 $112.55   8.786%   $122.4386   $122.44   $122.45   $122.40  
  7 purchase totals = $658.89       $709.5445   $709.54   $709.60   $709.40