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 $95.79   8.767%   $104.1879   $104.19   $104.20   $104.20  
  Purchase #2 $157.61   12.377%   $177.1174   $177.12   $177.10   $177.10  
  Purchase #3 $35.98   11.353%   $40.0648   $40.06   $40.05   $40.10  
  Purchase #4 $196.90   6.655%   $210.0037   $210.00   $210.00   $210.00  
  Purchase #5 $208.46   11.797%   $233.052   $233.05   $233.05   $233.10  
  Purchase #6 $90.46   6.528%   $96.3652   $96.37   $96.35   $96.40  
  Purchase #7 $67.88   12.229%   $76.181   $76.18   $76.20   $76.20  
  7 purchase totals = $853.08       $936.9720   $936.97   $936.95   $937.10