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 $62.73   7.168%   $67.2265   $67.23   $67.25   $67.20  
  Purchase #2 $53.98   3.373%   $55.8007   $55.80   $55.80   $55.80  
  Purchase #3 $46.86   5.523%   $49.4481   $49.45   $49.45   $49.40  
  Purchase #4 $67.49   3.217%   $69.6612   $69.66   $69.65   $69.70  
  Purchase #5 $23.47   12.251%   $26.3453   $26.35   $26.35   $26.30  
  Purchase #6 $95.81   5.441%   $101.023   $101.02   $101.00   $101.00  
  Purchase #7 $64.41   4.487%   $67.3001   $67.30   $67.30   $67.30  
  7 purchase totals = $414.75       $436.8049   $436.81   $436.80   $436.70