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 $218.95   6.201%   $232.5271   $232.53   $232.55   $232.50  
  Purchase #2 $78.92   12.650%   $88.9034   $88.90   $88.90   $88.90  
  Purchase #3 $55.45   12.539%   $62.4029   $62.40   $62.40   $62.40  
  Purchase #4 $29.88   6.484%   $31.8174   $31.82   $31.80   $31.80  
  Purchase #5 $202.64   8.102%   $219.0579   $219.06   $219.05   $219.10  
  Purchase #6 $200.42   3.104%   $206.641   $206.64   $206.65   $206.60  
  Purchase #7 $213.39   6.102%   $226.4111   $226.41   $226.40   $226.40  
  7 purchase totals = $999.65       $1,067.7608   $1,067.76   $1,067.75   $1,067.70