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 $208.68   8.584%   $226.5931   $226.59   $226.60   $226.60  
  Purchase #2 $141.79   3.454%   $146.6874   $146.69   $146.70   $146.70  
  Purchase #3 $48.76   12.594%   $54.9008   $54.90   $54.90   $54.90  
  Purchase #4 $170.93   12.517%   $192.3253   $192.33   $192.35   $192.30  
  Purchase #5 $119.88   9.249%   $130.9677   $130.97   $130.95   $131.00  
  Purchase #6 $171.89   9.295%   $187.8672   $187.87   $187.85   $187.90  
  Purchase #7 $181.66   11.112%   $201.8461   $201.85   $201.85   $201.80  
  7 purchase totals = $1,043.59       $1,141.1876   $1,141.20   $1,141.20   $1,141.20