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 $244.29   10.211%   $269.2345   $269.23   $269.25   $269.20  
  Purchase #2 $238.95   13.174%   $270.4293   $270.43   $270.45   $270.40  
  Purchase #3 $110.84   8.495%   $120.2559   $120.26   $120.25   $120.30  
  Purchase #4 $166.47   12.686%   $187.5884   $187.59   $187.60   $187.60  
  Purchase #5 $91.35   11.123%   $101.5109   $101.51   $101.50   $101.50  
  Purchase #6 $126.66   5.232%   $133.2869   $133.29   $133.30   $133.30  
  Purchase #7 $168.77   6.564%   $179.8481   $179.85   $179.85   $179.80  
  7 purchase totals = $1,147.33       $1,262.1540   $1,262.16   $1,262.20   $1,262.10