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 $144.62   11.510%   $161.2658   $161.27   $161.25   $161.30  
  Purchase #2 $77.61   5.210%   $81.6535   $81.65   $81.65   $81.70  
  Purchase #3 $233.81   13.320%   $264.9535   $264.95   $264.95   $265.00  
  Purchase #4 $22.26   11.759%   $24.8776   $24.88   $24.90   $24.90  
  Purchase #5 $113.27   12.646%   $127.5941   $127.59   $127.60   $127.60  
  Purchase #6 $149.36   6.649%   $159.2909   $159.29   $159.30   $159.30  
  Purchase #7 $66.86   11.670%   $74.6626   $74.66   $74.65   $74.70  
  7 purchase totals = $807.79       $894.2980   $894.29   $894.30   $894.50