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 $57.83   4.167%   $60.2398   $60.24   $60.25   $60.20  
  Purchase #2 $172.29   13.527%   $195.5957   $195.60   $195.60   $195.60  
  Purchase #3 $101.89   6.615%   $108.63   $108.63   $108.65   $108.60  
  Purchase #4 $51.75   9.150%   $56.4851   $56.49   $56.50   $56.50  
  Purchase #5 $202.93   8.817%   $220.8223   $220.82   $220.80   $220.80  
  Purchase #6 $33.61   12.320%   $37.7508   $37.75   $37.75   $37.80  
  Purchase #7 $80.43   5.465%   $84.8255   $84.83   $84.85   $84.80  
  7 purchase totals = $700.73       $764.3492   $764.36   $764.40   $764.30