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 $184.29   6.267%   $195.8395   $195.84   $195.85   $195.80  
  Purchase #2 $32.67   3.560%   $33.8331   $33.83   $33.85   $33.80  
  Purchase #3 $116.38   5.117%   $122.3352   $122.34   $122.35   $122.30  
  Purchase #4 $157.63   3.200%   $162.6742   $162.67   $162.65   $162.70  
  Purchase #5 $213.26   10.874%   $236.4499   $236.45   $236.45   $236.40  
  Purchase #6 $151.25   8.436%   $164.0095   $164.01   $164.00   $164.00  
  Purchase #7 $53.28   6.689%   $56.8439   $56.84   $56.85   $56.80  
  7 purchase totals = $908.76       $971.9853   $971.98   $972.00   $971.80