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 $91.34   6.128%   $96.9373   $96.94   $96.95   $96.90  
  Purchase #2 $203.59   5.533%   $214.8546   $214.85   $214.85   $214.90  
  Purchase #3 $109.28   10.637%   $120.9041   $120.90   $120.90   $120.90  
  Purchase #4 $77.96   7.212%   $83.5825   $83.58   $83.60   $83.60  
  Purchase #5 $48.96   9.674%   $53.6964   $53.70   $53.70   $53.70  
  Purchase #6 $224.57   8.721%   $244.1547   $244.15   $244.15   $244.20  
  Purchase #7 $201.84   8.786%   $219.5737   $219.57   $219.55   $219.60  
  7 purchase totals = $957.54       $1,033.7033   $1,033.69   $1,033.70   $1,033.80