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 $61.68   6.736%   $65.8348   $65.83   $65.85   $65.80  
  Purchase #2 $187.99   11.520%   $209.6464   $209.65   $209.65   $209.60  
  Purchase #3 $116.85   5.618%   $123.4146   $123.41   $123.40   $123.40  
  Purchase #4 $98.52   10.583%   $108.9464   $108.95   $108.95   $108.90  
  Purchase #5 $215.52   8.494%   $233.8263   $233.83   $233.85   $233.80  
  Purchase #6 $106.74   13.571%   $121.2257   $121.23   $121.25   $121.20  
  Purchase #7 $186.69   9.460%   $204.3509   $204.35   $204.35   $204.40  
  7 purchase totals = $973.99       $1,067.2451   $1,067.25   $1,067.30   $1,067.10