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 $129.64   12.627%   $146.0096   $146.01   $146.00   $146.00  
  Purchase #2 $149.86   9.216%   $163.6711   $163.67   $163.65   $163.70  
  Purchase #3 $45.61   9.625%   $50   $50.00   $50.00   $50.00  
  Purchase #4 $242.69   8.860%   $264.1923   $264.19   $264.20   $264.20  
  Purchase #5 $183.80   10.819%   $203.6853   $203.69   $203.70   $203.70  
  Purchase #6 $25.32   4.556%   $26.4736   $26.47   $26.45   $26.50  
  Purchase #7 $88.67   11.211%   $98.6108   $98.61   $98.60   $98.60  
  7 purchase totals = $865.59       $952.6427   $952.64   $952.60   $952.70