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 $41.34   7.352%   $44.3793   $44.38   $44.40   $44.40  
  Purchase #2 $24.59   12.490%   $27.6613   $27.66   $27.65   $27.70  
  Purchase #3 $117.49   7.749%   $126.5943   $126.59   $126.60   $126.60  
  Purchase #4 $137.93   13.291%   $156.2623   $156.26   $156.25   $156.30  
  Purchase #5 $52.38   11.701%   $58.509   $58.51   $58.50   $58.50  
  Purchase #6 $193.89   5.137%   $203.8501   $203.85   $203.85   $203.90  
  Purchase #7 $242.88   9.117%   $265.0234   $265.02   $265.00   $265.00  
  7 purchase totals = $810.50       $882.2797   $882.27   $882.25   $882.40