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 $213.68   6.139%   $226.7978   $226.80   $226.80   $226.80  
  Purchase #2 $64.54   11.366%   $71.8756   $71.88   $71.90   $71.90  
  Purchase #3 $205.46   6.292%   $218.3875   $218.39   $218.40   $218.40  
  Purchase #4 $22.40   4.268%   $23.356   $23.36   $23.35   $23.40  
  Purchase #5 $209.69   12.827%   $236.5869   $236.59   $236.60   $236.60  
  Purchase #6 $86.51   3.688%   $89.7005   $89.70   $89.70   $89.70  
  Purchase #7 $52.25   11.764%   $58.3967   $58.40   $58.40   $58.40  
  7 purchase totals = $854.53       $925.1010   $925.12   $925.15   $925.20