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 $110.42   3.263%   $114.023   $114.02   $114.00   $114.00  
  Purchase #2 $62.28   9.739%   $68.3454   $68.35   $68.35   $68.30  
  Purchase #3 $150.42   12.263%   $168.866   $168.87   $168.85   $168.90  
  Purchase #4 $122.59   9.251%   $133.9308   $133.93   $133.95   $133.90  
  Purchase #5 $231.25   12.614%   $260.4199   $260.42   $260.40   $260.40  
  Purchase #6 $196.53   4.660%   $205.6883   $205.69   $205.70   $205.70  
  Purchase #7 $24.91   3.796%   $25.8556   $25.86   $25.85   $25.90  
  7 purchase totals = $898.40       $977.1290   $977.14   $977.10   $977.10