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 $89.74   6.261%   $95.3586   $95.36   $95.35   $95.40  
  Purchase #2 $218.76   10.284%   $241.2573   $241.26   $241.25   $241.30  
  Purchase #3 $56.28   3.461%   $58.2279   $58.23   $58.25   $58.20  
  Purchase #4 $19.93   6.575%   $21.2404   $21.24   $21.25   $21.20  
  Purchase #5 $111.87   12.813%   $126.2039   $126.20   $126.20   $126.20  
  Purchase #6 $243.49   12.727%   $274.479   $274.48   $274.50   $274.50  
  Purchase #7 $218.81   10.427%   $241.6253   $241.63   $241.65   $241.60  
  7 purchase totals = $958.88       $1,058.3924   $1,058.40   $1,058.45   $1,058.40