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 $71.97   8.170%   $77.8499   $77.85   $77.85   $77.80  
  Purchase #2 $183.84   9.688%   $201.6504   $201.65   $201.65   $201.70  
  Purchase #3 $165.64   6.337%   $176.1366   $176.14   $176.15   $176.10  
  Purchase #4 $146.74   10.402%   $162.0039   $162.00   $162.00   $162.00  
  Purchase #5 $100.68   3.712%   $104.4172   $104.42   $104.40   $104.40  
  Purchase #6 $61.57   9.382%   $67.3465   $67.35   $67.35   $67.30  
  Purchase #7 $83.95   13.673%   $95.4285   $95.43   $95.45   $95.40  
  7 purchase totals = $814.39       $884.8330   $884.84   $884.85   $884.70