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 $34.89   4.651%   $36.5127   $36.51   $36.50   $36.50  
  Purchase #2 $182.83   10.595%   $202.2008   $202.20   $202.20   $202.20  
  Purchase #3 $49.62   13.869%   $56.5018   $56.50   $56.50   $56.50  
  Purchase #4 $170.71   6.647%   $182.0571   $182.06   $182.05   $182.10  
  Purchase #5 $234.66   5.624%   $247.8573   $247.86   $247.85   $247.90  
  Purchase #6 $240.93   11.229%   $267.984   $267.98   $268.00   $268.00  
  Purchase #7 $69.41   6.483%   $73.9099   $73.91   $73.90   $73.90  
  7 purchase totals = $983.05       $1,067.0236   $1,067.02   $1,067.00   $1,067.10