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 $244.73   8.530%   $265.6055   $265.61   $265.60   $265.60  
  Purchase #2 $161.96   12.219%   $181.7499   $181.75   $181.75   $181.70  
  Purchase #3 $168.70   13.492%   $191.461   $191.46   $191.45   $191.50  
  Purchase #4 $47.80   9.531%   $52.3558   $52.36   $52.35   $52.40  
  Purchase #5 $52.81   5.474%   $55.7008   $55.70   $55.70   $55.70  
  Purchase #6 $236.83   4.551%   $247.6081   $247.61   $247.60   $247.60  
  Purchase #7 $128.49   4.188%   $133.8712   $133.87   $133.85   $133.90  
  7 purchase totals = $1,041.32       $1,128.3523   $1,128.36   $1,128.30   $1,128.40