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 $250.92   6.862%   $268.1381   $268.14   $268.15   $268.10  
  Purchase #2 $188.70   11.840%   $211.0421   $211.04   $211.05   $211.00  
  Purchase #3 $225.48   12.773%   $254.2806   $254.28   $254.30   $254.30  
  Purchase #4 $36.36   6.772%   $38.8223   $38.82   $38.80   $38.80  
  Purchase #5 $148.30   6.376%   $157.7556   $157.76   $157.75   $157.80  
  Purchase #6 $186.63   7.698%   $200.9968   $201.00   $201.00   $201.00  
  Purchase #7 $42.75   7.244%   $45.8468   $45.85   $45.85   $45.80  
  7 purchase totals = $1,079.14       $1,176.8823   $1,176.89   $1,176.90   $1,176.80