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 $220.34   5.429%   $232.3023   $232.30   $232.30   $232.30  
  Purchase #2 $137.51   13.628%   $156.2499   $156.25   $156.25   $156.20  
  Purchase #3 $162.86   12.487%   $183.1963   $183.20   $183.20   $183.20  
  Purchase #4 $121.44   4.593%   $127.0177   $127.02   $127.00   $127.00  
  Purchase #5 $41.93   13.434%   $47.5629   $47.56   $47.55   $47.60  
  Purchase #6 $48.34   9.263%   $52.8177   $52.82   $52.80   $52.80  
  Purchase #7 $227.89   9.812%   $250.2506   $250.25   $250.25   $250.30  
  7 purchase totals = $960.31       $1,049.3974   $1,049.40   $1,049.35   $1,049.40