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 $42.59   10.459%   $47.0445   $47.04   $47.05   $47.00  
  Purchase #2 $55.73   7.609%   $59.9705   $59.97   $59.95   $60.00  
  Purchase #3 $11.36   3.440%   $11.7508   $11.75   $11.75   $11.80  
  Purchase #4 $29.49   12.508%   $33.1786   $33.18   $33.20   $33.20  
  Purchase #5 $95.28   3.255%   $98.3814   $98.38   $98.40   $98.40  
  Purchase #6 $212.67   13.796%   $242.01   $242.01   $242.00   $242.00  
  Purchase #7 $135.37   3.159%   $139.6463   $139.65   $139.65   $139.60  
  7 purchase totals = $582.49       $631.9821   $631.98   $632.00   $632.00