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 $245.73   8.232%   $265.9585   $265.96   $265.95   $266.00  
  Purchase #2 $56.65   5.254%   $59.6264   $59.63   $59.65   $59.60  
  Purchase #3 $126.92   5.332%   $133.6874   $133.69   $133.70   $133.70  
  Purchase #4 $207.49   11.842%   $232.061   $232.06   $232.05   $232.10  
  Purchase #5 $109.40   6.532%   $116.546   $116.55   $116.55   $116.50  
  Purchase #6 $24.65   13.767%   $28.0436   $28.04   $28.05   $28.00  
  Purchase #7 $155.63   10.566%   $172.0739   $172.07   $172.05   $172.10  
  7 purchase totals = $926.47       $1,007.9968   $1,008.00   $1,008.00   $1,008.00