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 $24.97   7.534%   $26.8512   $26.85   $26.85   $26.90  
  Purchase #2 $59.55   12.548%   $67.0223   $67.02   $67.00   $67.00  
  Purchase #3 $250.70   4.873%   $262.9166   $262.92   $262.90   $262.90  
  Purchase #4 $192.37   11.219%   $213.952   $213.95   $213.95   $214.00  
  Purchase #5 $124.51   7.253%   $133.5407   $133.54   $133.55   $133.50  
  Purchase #6 $46.63   7.828%   $50.2802   $50.28   $50.30   $50.30  
  Purchase #7 $29.79   10.121%   $32.805   $32.81   $32.80   $32.80  
  7 purchase totals = $728.52       $787.3680   $787.37   $787.35   $787.40