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 $12.82   10.692%   $14.1907   $14.19   $14.20   $14.20  
  Purchase #2 $227.77   6.408%   $242.3655   $242.37   $242.35   $242.40  
  Purchase #3 $134.67   11.156%   $149.6938   $149.69   $149.70   $149.70  
  Purchase #4 $211.73   11.840%   $236.7988   $236.80   $236.80   $236.80  
  Purchase #5 $113.87   12.797%   $128.4419   $128.44   $128.45   $128.40  
  Purchase #6 $186.70   3.203%   $192.68   $192.68   $192.70   $192.70  
  Purchase #7 $236.93   7.705%   $255.1855   $255.19   $255.20   $255.20  
  7 purchase totals = $1,124.49       $1,219.3562   $1,219.36   $1,219.40   $1,219.40