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 $126.64   6.199%   $134.4904   $134.49   $134.50   $134.50  
  Purchase #2 $193.83   13.329%   $219.6656   $219.67   $219.65   $219.70  
  Purchase #3 $249.43   8.677%   $271.073   $271.07   $271.05   $271.10  
  Purchase #4 $85.85   12.604%   $96.6705   $96.67   $96.65   $96.70  
  Purchase #5 $184.68   12.528%   $207.8167   $207.82   $207.80   $207.80  
  Purchase #6 $181.54   13.790%   $206.5744   $206.57   $206.55   $206.60  
  Purchase #7 $214.99   9.350%   $235.0916   $235.09   $235.10   $235.10  
  7 purchase totals = $1,236.96       $1,371.3822   $1,371.38   $1,371.30   $1,371.50