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 $58.68   11.494%   $65.4247   $65.42   $65.40   $65.40  
  Purchase #2 $162.31   10.185%   $178.8413   $178.84   $178.85   $178.80  
  Purchase #3 $246.81   7.540%   $265.4195   $265.42   $265.40   $265.40  
  Purchase #4 $89.31   7.554%   $96.0565   $96.06   $96.05   $96.10  
  Purchase #5 $218.59   6.129%   $231.9874   $231.99   $232.00   $232.00  
  Purchase #6 $231.69   7.867%   $249.9171   $249.92   $249.90   $249.90  
  Purchase #7 $135.68   5.427%   $143.0434   $143.04   $143.05   $143.00  
  7 purchase totals = $1,143.07       $1,230.6899   $1,230.69   $1,230.65   $1,230.60