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 $142.90   13.787%   $162.6016   $162.60   $162.60   $162.60  
  Purchase #2 $200.41   10.558%   $221.5693   $221.57   $221.55   $221.60  
  Purchase #3 $245.70   13.558%   $279.012   $279.01   $279.00   $279.00  
  Purchase #4 $60.62   9.811%   $66.5674   $66.57   $66.55   $66.60  
  Purchase #5 $5.97   3.523%   $6.1803   $6.18   $6.20   $6.20  
  Purchase #6 $248.72   6.573%   $265.0684   $265.07   $265.05   $265.10  
  Purchase #7 $11.60   11.314%   $12.9124   $12.91   $12.90   $12.90  
  7 purchase totals = $915.92       $1,013.9114   $1,013.91   $1,013.85   $1,014.00