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 $106.69   10.477%   $117.8679   $117.87   $117.85   $117.90  
  Purchase #2 $155.41   13.662%   $176.6421   $176.64   $176.65   $176.60  
  Purchase #3 $215.35   12.276%   $241.7864   $241.79   $241.80   $241.80  
  Purchase #4 $126.89   4.722%   $132.8817   $132.88   $132.90   $132.90  
  Purchase #5 $239.31   13.683%   $272.0548   $272.05   $272.05   $272.10  
  Purchase #6 $42.47   4.161%   $44.2372   $44.24   $44.25   $44.20  
  Purchase #7 $69.56   7.827%   $75.0045   $75.00   $75.00   $75.00  
  7 purchase totals = $955.68       $1,060.4746   $1,060.47   $1,060.50   $1,060.50