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 $22.76   6.768%   $24.3004   $24.30   $24.30   $24.30  
  Purchase #2 $179.44   13.602%   $203.8474   $203.85   $203.85   $203.80  
  Purchase #3 $97.63   9.727%   $107.1265   $107.13   $107.15   $107.10  
  Purchase #4 $126.28   12.585%   $142.1723   $142.17   $142.15   $142.20  
  Purchase #5 $241.55   10.715%   $267.4321   $267.43   $267.45   $267.40  
  Purchase #6 $136.88   13.791%   $155.7571   $155.76   $155.75   $155.80  
  Purchase #7 $80.44   8.395%   $87.1929   $87.19   $87.20   $87.20  
  7 purchase totals = $884.98       $987.8287   $987.83   $987.85   $987.80