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 $50.28   8.699%   $54.6539   $54.65   $54.65   $54.70  
  Purchase #2 $185.57   9.593%   $203.3717   $203.37   $203.35   $203.40  
  Purchase #3 $207.47   5.608%   $219.1049   $219.10   $219.10   $219.10  
  Purchase #4 $27.77   9.456%   $30.3959   $30.40   $30.40   $30.40  
  Purchase #5 $178.31   11.830%   $199.4041   $199.40   $199.40   $199.40  
  Purchase #6 $129.76   5.565%   $136.9811   $136.98   $137.00   $137.00  
  Purchase #7 $214.87   8.733%   $233.6346   $233.63   $233.65   $233.60  
  7 purchase totals = $994.03       $1,077.5462   $1,077.53   $1,077.55   $1,077.60