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 $208.69   3.641%   $216.2884   $216.29   $216.30   $216.30  
  Purchase #2 $54.49   11.860%   $60.9525   $60.95   $60.95   $61.00  
  Purchase #3 $136.37   11.540%   $152.1071   $152.11   $152.10   $152.10  
  Purchase #4 $9.98   3.692%   $10.3485   $10.35   $10.35   $10.30  
  Purchase #5 $95.54   11.793%   $106.807   $106.81   $106.80   $106.80  
  Purchase #6 $244.70   8.452%   $265.382   $265.38   $265.40   $265.40  
  Purchase #7 $127.97   8.113%   $138.3522   $138.35   $138.35   $138.40  
  7 purchase totals = $877.74       $950.2377   $950.24   $950.25   $950.30