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 $31.95   11.228%   $35.5373   $35.54   $35.55   $35.50  
  Purchase #2 $49.85   7.592%   $53.6346   $53.63   $53.65   $53.60  
  Purchase #3 $215.99   8.546%   $234.4485   $234.45   $234.45   $234.40  
  Purchase #4 $178.79   9.333%   $195.4765   $195.48   $195.50   $195.50  
  Purchase #5 $124.99   9.564%   $136.944   $136.94   $136.95   $136.90  
  Purchase #6 $244.88   4.103%   $254.9274   $254.93   $254.95   $254.90  
  Purchase #7 $150.50   4.613%   $157.4426   $157.44   $157.45   $157.40  
  7 purchase totals = $996.95       $1,068.4109   $1,068.41   $1,068.50   $1,068.20