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 $58.82   10.469%   $64.9779   $64.98   $65.00   $65.00  
  Purchase #2 $65.59   9.623%   $71.9017   $71.90   $71.90   $71.90  
  Purchase #3 $234.30   8.808%   $254.9371   $254.94   $254.95   $254.90  
  Purchase #4 $209.29   12.850%   $236.1838   $236.18   $236.20   $236.20  
  Purchase #5 $82.96   4.656%   $86.8226   $86.82   $86.80   $86.80  
  Purchase #6 $92.50   3.672%   $95.8966   $95.90   $95.90   $95.90  
  Purchase #7 $19.50   9.368%   $21.3268   $21.33   $21.35   $21.30  
  7 purchase totals = $762.96       $832.0465   $832.05   $832.10   $832.00