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 $65.28   5.437%   $68.8293   $68.83   $68.85   $68.80  
  Purchase #2 $32.48   4.634%   $33.9851   $33.99   $34.00   $34.00  
  Purchase #3 $33.42   9.155%   $36.4796   $36.48   $36.50   $36.50  
  Purchase #4 $214.75   5.477%   $226.5119   $226.51   $226.50   $226.50  
  Purchase #5 $247.49   8.547%   $268.643   $268.64   $268.65   $268.60  
  Purchase #6 $194.61   3.256%   $200.9465   $200.95   $200.95   $200.90  
  Purchase #7 $146.35   13.771%   $166.5039   $166.50   $166.50   $166.50  
  7 purchase totals = $934.38       $1,001.8993   $1,001.90   $1,001.95   $1,001.80