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 $98.37   5.652%   $103.9299   $103.93   $103.95   $103.90  
  Purchase #2 $187.46   8.263%   $202.9498   $202.95   $202.95   $202.90  
  Purchase #3 $113.87   11.562%   $127.0356   $127.04   $127.05   $127.00  
  Purchase #4 $160.97   12.596%   $181.2458   $181.25   $181.25   $181.20  
  Purchase #5 $205.25   9.548%   $224.8473   $224.85   $224.85   $224.80  
  Purchase #6 $39.26   7.722%   $42.2917   $42.29   $42.30   $42.30  
  Purchase #7 $64.73   4.681%   $67.76   $67.76   $67.75   $67.80  
  7 purchase totals = $869.91       $950.0601   $950.07   $950.10   $949.90