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 $54.41   13.843%   $61.942   $61.94   $61.95   $61.90  
  Purchase #2 $14.46   7.856%   $15.596   $15.60   $15.60   $15.60  
  Purchase #3 $203.98   13.192%   $230.889   $230.89   $230.90   $230.90  
  Purchase #4 $111.70   12.447%   $125.6033   $125.60   $125.60   $125.60  
  Purchase #5 $14.46   11.658%   $16.1457   $16.15   $16.15   $16.10  
  Purchase #6 $67.76   13.337%   $76.7972   $76.80   $76.80   $76.80  
  Purchase #7 $57.26   11.529%   $63.8615   $63.86   $63.85   $63.90  
  7 purchase totals = $524.03       $590.8347   $590.84   $590.85   $590.80