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 $240.37   13.495%   $272.8079   $272.81   $272.80   $272.80  
  Purchase #2 $94.35   4.393%   $98.4948   $98.49   $98.50   $98.50  
  Purchase #3 $42.43   6.617%   $45.2376   $45.24   $45.25   $45.20  
  Purchase #4 $154.35   13.207%   $174.735   $174.74   $174.75   $174.70  
  Purchase #5 $236.65   11.463%   $263.7772   $263.78   $263.80   $263.80  
  Purchase #6 $126.81   6.316%   $134.8193   $134.82   $134.80   $134.80  
  Purchase #7 $67.97   3.620%   $70.4305   $70.43   $70.45   $70.40  
  7 purchase totals = $962.93       $1,060.3023   $1,060.31   $1,060.35   $1,060.20