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 $245.94   3.690%   $255.0152   $255.02   $255.00   $255.00  
  Purchase #2 $197.37   4.686%   $206.6188   $206.62   $206.60   $206.60  
  Purchase #3 $163.70   4.633%   $171.2842   $171.28   $171.30   $171.30  
  Purchase #4 $74.85   5.286%   $78.8066   $78.81   $78.80   $78.80  
  Purchase #5 $20.48   10.378%   $22.6054   $22.61   $22.60   $22.60  
  Purchase #6 $113.26   10.279%   $124.902   $124.90   $124.90   $124.90  
  Purchase #7 $155.46   7.873%   $167.6994   $167.70   $167.70   $167.70  
  7 purchase totals = $971.06       $1,026.9316   $1,026.94   $1,026.90   $1,026.90