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 $91.93   3.376%   $95.0336   $95.03   $95.05   $95.00  
  Purchase #2 $5.93   11.470%   $6.6102   $6.61   $6.60   $6.60  
  Purchase #3 $141.53   3.335%   $146.25   $146.25   $146.25   $146.30  
  Purchase #4 $18.38   6.496%   $19.574   $19.57   $19.55   $19.60  
  Purchase #5 $15.93   7.286%   $17.0907   $17.09   $17.10   $17.10  
  Purchase #6 $126.46   13.673%   $143.7509   $143.75   $143.75   $143.80  
  Purchase #7 $158.70   5.816%   $167.93   $167.93   $167.95   $167.90  
  7 purchase totals = $558.86       $596.2394   $596.23   $596.25   $596.30