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 $136.76   13.501%   $155.224   $155.22   $155.20   $155.20  
  Purchase #2 $193.98   3.686%   $201.1301   $201.13   $201.15   $201.10  
  Purchase #3 $220.39   6.464%   $234.636   $234.64   $234.65   $234.60  
  Purchase #4 $239.71   12.404%   $269.4436   $269.44   $269.45   $269.40  
  Purchase #5 $129.84   13.167%   $146.936   $146.94   $146.95   $146.90  
  Purchase #6 $23.69   3.172%   $24.4414   $24.44   $24.45   $24.40  
  Purchase #7 $15.46   13.497%   $17.5466   $17.55   $17.55   $17.50  
  7 purchase totals = $959.83       $1,049.3577   $1,049.36   $1,049.40   $1,049.10