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 $218.75   10.283%   $241.2441   $241.24   $241.25   $241.20  
  Purchase #2 $209.62   7.388%   $225.1067   $225.11   $225.10   $225.10  
  Purchase #3 $33.41   10.250%   $36.8345   $36.83   $36.85   $36.80  
  Purchase #4 $65.56   4.256%   $68.3502   $68.35   $68.35   $68.40  
  Purchase #5 $211.67   13.147%   $239.4983   $239.50   $239.50   $239.50  
  Purchase #6 $218.51   5.423%   $230.3598   $230.36   $230.35   $230.40  
  Purchase #7 $147.31   8.833%   $160.3219   $160.32   $160.30   $160.30  
  7 purchase totals = $1,104.83       $1,201.7155   $1,201.71   $1,201.70   $1,201.70