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 $61.52   13.449%   $69.7938   $69.79   $69.80   $69.80  
  Purchase #2 $188.58   10.279%   $207.9641   $207.96   $207.95   $208.00  
  Purchase #3 $49.77   7.193%   $53.35   $53.35   $53.35   $53.40  
  Purchase #4 $92.70   4.208%   $96.6008   $96.60   $96.60   $96.60  
  Purchase #5 $26.83   5.619%   $28.3376   $28.34   $28.35   $28.30  
  Purchase #6 $158.60   3.426%   $164.0336   $164.03   $164.05   $164.00  
  Purchase #7 $33.60   8.543%   $36.4704   $36.47   $36.45   $36.50  
  7 purchase totals = $611.60       $656.5503   $656.54   $656.55   $656.60