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 $86.51   9.448%   $94.6835   $94.68   $94.70   $94.70  
  Purchase #2 $125.55   6.177%   $133.3052   $133.31   $133.30   $133.30  
  Purchase #3 $67.63   11.671%   $75.5231   $75.52   $75.50   $75.50  
  Purchase #4 $246.83   9.763%   $270.928   $270.93   $270.95   $270.90  
  Purchase #5 $142.26   4.821%   $149.1184   $149.12   $149.10   $149.10  
  Purchase #6 $98.59   10.351%   $108.7951   $108.80   $108.80   $108.80  
  Purchase #7 $214.30   8.148%   $231.7612   $231.76   $231.75   $231.80  
  7 purchase totals = $981.67       $1,064.1145   $1,064.12   $1,064.10   $1,064.10