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 $161.33   9.268%   $176.2821   $176.28   $176.30   $176.30  
  Purchase #2 $48.99   3.534%   $50.7213   $50.72   $50.70   $50.70  
  Purchase #3 $79.39   5.306%   $83.6024   $83.60   $83.60   $83.60  
  Purchase #4 $55.98   6.544%   $59.6433   $59.64   $59.65   $59.60  
  Purchase #5 $63.60   6.741%   $67.8873   $67.89   $67.90   $67.90  
  Purchase #6 $192.32   8.496%   $208.6595   $208.66   $208.65   $208.70  
  Purchase #7 $203.25   8.874%   $221.2864   $221.29   $221.30   $221.30  
  7 purchase totals = $804.86       $868.0823   $868.08   $868.10   $868.10