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 $130.36   4.205%   $135.8416   $135.84   $135.85   $135.80  
  Purchase #2 $36.42   5.684%   $38.4901   $38.49   $38.50   $38.50  
  Purchase #3 $162.72   6.174%   $172.7663   $172.77   $172.75   $172.80  
  Purchase #4 $156.72   3.569%   $162.3133   $162.31   $162.30   $162.30  
  Purchase #5 $18.83   10.739%   $20.8522   $20.85   $20.85   $20.90  
  Purchase #6 $11.93   8.286%   $12.9185   $12.92   $12.90   $12.90  
  Purchase #7 $170.81   4.171%   $177.9345   $177.93   $177.95   $177.90  
  7 purchase totals = $687.79       $721.1165   $721.11   $721.10   $721.10