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 $97.94   6.652%   $104.455   $104.46   $104.45   $104.50  
  Purchase #2 $243.47   5.631%   $257.1798   $257.18   $257.20   $257.20  
  Purchase #3 $83.79   3.274%   $86.5333   $86.53   $86.55   $86.50  
  Purchase #4 $56.68   7.804%   $61.1033   $61.10   $61.10   $61.10  
  Purchase #5 $215.90   3.117%   $222.6296   $222.63   $222.65   $222.60  
  Purchase #6 $197.53   10.797%   $218.8573   $218.86   $218.85   $218.90  
  Purchase #7 $181.94   11.305%   $202.5083   $202.51   $202.50   $202.50  
  7 purchase totals = $1,077.25       $1,153.2666   $1,153.27   $1,153.30   $1,153.30