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 $240.85   9.579%   $263.921   $263.92   $263.90   $263.90  
  Purchase #2 $65.93   7.443%   $70.8372   $70.84   $70.85   $70.80  
  Purchase #3 $86.30   6.819%   $92.1848   $92.18   $92.20   $92.20  
  Purchase #4 $182.49   11.419%   $203.3285   $203.33   $203.35   $203.30  
  Purchase #5 $131.55   7.229%   $141.0597   $141.06   $141.05   $141.10  
  Purchase #6 $72.46   10.442%   $80.0263   $80.03   $80.05   $80.00  
  Purchase #7 $30.36   11.436%   $33.832   $33.83   $33.85   $33.80  
  7 purchase totals = $809.94       $885.1895   $885.19   $885.25   $885.10