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 $204.77   3.149%   $211.2182   $211.22   $211.20   $211.20  
  Purchase #2 $176.27   9.814%   $193.5691   $193.57   $193.55   $193.60  
  Purchase #3 $239.27   5.481%   $252.3844   $252.38   $252.40   $252.40  
  Purchase #4 $212.46   11.372%   $236.621   $236.62   $236.60   $236.60  
  Purchase #5 $239.50   3.446%   $247.7532   $247.75   $247.75   $247.80  
  Purchase #6 $239.81   13.572%   $272.357   $272.36   $272.35   $272.40  
  Purchase #7 $211.73   3.596%   $219.3438   $219.34   $219.35   $219.30  
  7 purchase totals = $1,523.81       $1,633.2467   $1,633.24   $1,633.20   $1,633.30