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 $22.30   13.763%   $25.3691   $25.37   $25.35   $25.40  
  Purchase #2 $159.66   4.619%   $167.0347   $167.03   $167.05   $167.00  
  Purchase #3 $86.34   3.814%   $89.633   $89.63   $89.65   $89.60  
  Purchase #4 $53.30   3.513%   $55.1724   $55.17   $55.15   $55.20  
  Purchase #5 $89.95   7.479%   $96.6774   $96.68   $96.70   $96.70  
  Purchase #6 $121.88   3.409%   $126.0349   $126.03   $126.05   $126.00  
  Purchase #7 $38.88   9.835%   $42.7038   $42.70   $42.70   $42.70  
  7 purchase totals = $572.31       $602.6253   $602.61   $602.65   $602.60