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 $200.87   6.687%   $214.3022   $214.30   $214.30   $214.30  
  Purchase #2 $110.61   10.255%   $121.9531   $121.95   $121.95   $122.00  
  Purchase #3 $156.27   9.465%   $171.061   $171.06   $171.05   $171.10  
  Purchase #4 $56.70   4.378%   $59.1823   $59.18   $59.20   $59.20  
  Purchase #5 $150.59   4.267%   $157.0157   $157.02   $157.00   $157.00  
  Purchase #6 $243.86   10.627%   $269.775   $269.78   $269.80   $269.80  
  Purchase #7 $125.45   13.391%   $142.249   $142.25   $142.25   $142.20  
  7 purchase totals = $1,044.35       $1,135.5383   $1,135.54   $1,135.55   $1,135.60