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 $91.61   5.174%   $96.3499   $96.35   $96.35   $96.30  
  Purchase #2 $148.90   11.540%   $166.0831   $166.08   $166.10   $166.10  
  Purchase #3 $178.93   12.849%   $201.9207   $201.92   $201.90   $201.90  
  Purchase #4 $91.58   5.136%   $96.2835   $96.28   $96.30   $96.30  
  Purchase #5 $167.80   8.126%   $181.4354   $181.44   $181.45   $181.40  
  Purchase #6 $104.88   4.796%   $109.91   $109.91   $109.90   $109.90  
  Purchase #7 $194.60   9.778%   $213.628   $213.63   $213.65   $213.60  
  7 purchase totals = $978.30       $1,065.6106   $1,065.61   $1,065.65   $1,065.50