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 $23.51   10.429%   $25.9619   $25.96   $25.95   $26.00  
  Purchase #2 $250.46   6.828%   $267.5614   $267.56   $267.55   $267.60  
  Purchase #3 $108.85   6.487%   $115.9111   $115.91   $115.90   $115.90  
  Purchase #4 $145.69   3.421%   $150.6741   $150.67   $150.65   $150.70  
  Purchase #5 $225.84   6.744%   $241.0706   $241.07   $241.05   $241.10  
  Purchase #6 $61.53   13.126%   $69.6064   $69.61   $69.60   $69.60  
  Purchase #7 $80.86   8.227%   $87.5124   $87.51   $87.50   $87.50  
  7 purchase totals = $896.74       $958.2979   $958.29   $958.20   $958.40