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 $250.76   8.365%   $271.7361   $271.74   $271.75   $271.70  
  Purchase #2 $59.74   6.874%   $63.8465   $63.85   $63.85   $63.80  
  Purchase #3 $98.82   8.154%   $106.8778   $106.88   $106.90   $106.90  
  Purchase #4 $211.56   10.624%   $234.0361   $234.04   $234.05   $234.00  
  Purchase #5 $111.54   12.237%   $125.1891   $125.19   $125.20   $125.20  
  Purchase #6 $50.96   7.809%   $54.9395   $54.94   $54.95   $54.90  
  Purchase #7 $183.71   7.796%   $198.032   $198.03   $198.05   $198.00  
  7 purchase totals = $967.09       $1,054.6571   $1,054.67   $1,054.75   $1,054.50