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 $238.25   13.407%   $270.1922   $270.19   $270.20   $270.20  
  Purchase #2 $62.28   7.277%   $66.8121   $66.81   $66.80   $66.80  
  Purchase #3 $40.95   7.807%   $44.147   $44.15   $44.15   $44.10  
  Purchase #4 $98.44   6.212%   $104.5551   $104.56   $104.55   $104.60  
  Purchase #5 $219.70   4.163%   $228.8461   $228.85   $228.85   $228.80  
  Purchase #6 $177.44   4.400%   $185.2474   $185.25   $185.25   $185.20  
  Purchase #7 $184.43   12.319%   $207.1499   $207.15   $207.15   $207.10  
  7 purchase totals = $1,021.49       $1,106.9498   $1,106.96   $1,106.95   $1,106.80