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 $124.84   7.359%   $134.027   $134.03   $134.05   $134.00  
  Purchase #2 $243.69   9.239%   $266.2045   $266.20   $266.20   $266.20  
  Purchase #3 $83.25   4.464%   $86.9663   $86.97   $86.95   $87.00  
  Purchase #4 $189.42   7.535%   $203.6928   $203.69   $203.70   $203.70  
  Purchase #5 $39.73   4.800%   $41.637   $41.64   $41.65   $41.60  
  Purchase #6 $153.93   8.357%   $166.7939   $166.79   $166.80   $166.80  
  Purchase #7 $68.30   3.335%   $70.5778   $70.58   $70.60   $70.60  
  7 purchase totals = $903.16       $969.8993   $969.90   $969.95   $969.90