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 $76.71   9.243%   $83.8003   $83.80   $83.80   $83.80  
  Purchase #2 $196.25   11.646%   $219.1053   $219.11   $219.10   $219.10  
  Purchase #3 $163.94   4.596%   $171.4747   $171.47   $171.45   $171.50  
  Purchase #4 $170.77   11.432%   $190.2924   $190.29   $190.30   $190.30  
  Purchase #5 $181.48   3.594%   $188.0024   $188.00   $188.00   $188.00  
  Purchase #6 $196.82   5.692%   $208.023   $208.02   $208.00   $208.00  
  Purchase #7 $92.98   3.248%   $96   $96.00   $96.00   $96.00  
  7 purchase totals = $1,078.95       $1,156.6981   $1,156.69   $1,156.65   $1,156.70