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 $248.62   13.496%   $282.1738   $282.17   $282.15   $282.20  
  Purchase #2 $120.91   11.684%   $135.0371   $135.04   $135.05   $135.00  
  Purchase #3 $206.48   5.746%   $218.3443   $218.34   $218.35   $218.30  
  Purchase #4 $130.87   8.778%   $142.3578   $142.36   $142.35   $142.40  
  Purchase #5 $133.79   10.502%   $147.8406   $147.84   $147.85   $147.80  
  Purchase #6 $51.40   5.361%   $54.1556   $54.16   $54.15   $54.20  
  Purchase #7 $170.69   6.588%   $181.9351   $181.94   $181.95   $181.90  
  7 purchase totals = $1,062.76       $1,161.8443   $1,161.85   $1,161.85   $1,161.80