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 $186.86   5.162%   $196.5057   $196.51   $196.50   $196.50  
  Purchase #2 $71.91   9.796%   $78.9543   $78.95   $78.95   $79.00  
  Purchase #3 $243.73   10.308%   $268.8537   $268.85   $268.85   $268.90  
  Purchase #4 $206.26   7.476%   $221.68   $221.68   $221.70   $221.70  
  Purchase #5 $149.94   8.292%   $162.373   $162.37   $162.35   $162.40  
  Purchase #6 $179.70   12.799%   $202.6998   $202.70   $202.70   $202.70  
  Purchase #7 $87.43   12.122%   $98.0283   $98.03   $98.05   $98.00  
  7 purchase totals = $1,125.83       $1,229.0948   $1,229.09   $1,229.10   $1,229.20