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 $64.98   5.291%   $68.4181   $68.42   $68.40   $68.40  
  Purchase #2 $186.68   6.332%   $198.5006   $198.50   $198.50   $198.50  
  Purchase #3 $108.93   3.523%   $112.7676   $112.77   $112.75   $112.80  
  Purchase #4 $35.79   10.824%   $39.6639   $39.66   $39.65   $39.70  
  Purchase #5 $67.79   4.594%   $70.9043   $70.90   $70.90   $70.90  
  Purchase #6 $189.52   11.375%   $211.0779   $211.08   $211.10   $211.10  
  Purchase #7 $250.25   6.117%   $265.5578   $265.56   $265.55   $265.60  
  7 purchase totals = $903.94       $966.8902   $966.89   $966.85   $967.00