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 $72.67   11.579%   $81.0845   $81.08   $81.10   $81.10  
  Purchase #2 $77.83   9.222%   $85.0075   $85.01   $85.00   $85.00  
  Purchase #3 $248.33   9.351%   $271.5513   $271.55   $271.55   $271.60  
  Purchase #4 $238.85   7.505%   $256.7757   $256.78   $256.80   $256.80  
  Purchase #5 $175.98   13.835%   $200.3268   $200.33   $200.35   $200.30  
  Purchase #6 $82.90   4.712%   $86.8062   $86.81   $86.80   $86.80  
  Purchase #7 $166.43   9.357%   $182.0029   $182.00   $182.00   $182.00  
  7 purchase totals = $1,062.99       $1,163.5549   $1,163.56   $1,163.60   $1,163.60