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 $96.27   3.477%   $99.6173   $99.62   $99.60   $99.60  
  Purchase #2 $60.74   10.626%   $67.1942   $67.19   $67.20   $67.20  
  Purchase #3 $212.53   3.384%   $219.722   $219.72   $219.70   $219.70  
  Purchase #4 $131.91   5.214%   $138.7878   $138.79   $138.80   $138.80  
  Purchase #5 $99.57   7.839%   $107.3753   $107.38   $107.40   $107.40  
  Purchase #6 $123.41   8.543%   $133.9529   $133.95   $133.95   $134.00  
  Purchase #7 $27.84   5.174%   $29.2804   $29.28   $29.30   $29.30  
  7 purchase totals = $752.27       $795.9299   $795.93   $795.95   $796.00