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 $63.56   3.261%   $65.6327   $65.63   $65.65   $65.60  
  Purchase #2 $217.63   11.565%   $242.7989   $242.80   $242.80   $242.80  
  Purchase #3 $145.55   7.506%   $156.475   $156.48   $156.50   $156.50  
  Purchase #4 $226.81   9.683%   $248.772   $248.77   $248.75   $248.80  
  Purchase #5 $91.33   11.796%   $102.1033   $102.10   $102.10   $102.10  
  Purchase #6 $126.77   11.117%   $140.863   $140.86   $140.85   $140.90  
  Purchase #7 $18.39   13.407%   $20.8555   $20.86   $20.85   $20.90  
  7 purchase totals = $890.04       $977.5004   $977.50   $977.50   $977.60