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 $64.50   10.794%   $71.4621   $71.46   $71.45   $71.50  
  Purchase #2 $204.96   9.111%   $223.6339   $223.63   $223.65   $223.60  
  Purchase #3 $44.65   3.634%   $46.2726   $46.27   $46.25   $46.30  
  Purchase #4 $175.25   5.431%   $184.7678   $184.77   $184.75   $184.80  
  Purchase #5 $183.98   13.361%   $208.5616   $208.56   $208.55   $208.60  
  Purchase #6 $28.96   6.531%   $30.8514   $30.85   $30.85   $30.90  
  Purchase #7 $243.92   9.749%   $267.6998   $267.70   $267.70   $267.70  
  7 purchase totals = $946.22       $1,033.2492   $1,033.24   $1,033.20   $1,033.40