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 $17.41   13.292%   $19.7241   $19.72   $19.70   $19.70  
  Purchase #2 $234.85   9.171%   $256.3881   $256.39   $256.40   $256.40  
  Purchase #3 $126.70   4.215%   $132.0404   $132.04   $132.05   $132.00  
  Purchase #4 $192.88   9.692%   $211.5739   $211.57   $211.55   $211.60  
  Purchase #5 $16.76   13.296%   $18.9884   $18.99   $19.00   $19.00  
  Purchase #6 $58.73   4.874%   $61.5925   $61.59   $61.60   $61.60  
  Purchase #7 $50.79   6.122%   $53.8994   $53.90   $53.90   $53.90  
  7 purchase totals = $698.12       $754.2068   $754.20   $754.20   $754.20