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 $46.84   12.594%   $52.739   $52.74   $52.75   $52.70  
  Purchase #2 $31.63   7.244%   $33.9213   $33.92   $33.90   $33.90  
  Purchase #3 $137.49   3.673%   $142.54   $142.54   $142.55   $142.50  
  Purchase #4 $161.25   13.164%   $182.477   $182.48   $182.50   $182.50  
  Purchase #5 $246.59   4.484%   $257.6471   $257.65   $257.65   $257.60  
  Purchase #6 $184.32   12.336%   $207.0577   $207.06   $207.05   $207.10  
  Purchase #7 $168.49   11.579%   $187.9995   $188.00   $188.00   $188.00  
  7 purchase totals = $976.61       $1,064.3816   $1,064.39   $1,064.40   $1,064.30