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 $75.60   9.819%   $83.0232   $83.02   $83.00   $83.00  
  Purchase #2 $65.34   8.586%   $70.9501   $70.95   $70.95   $71.00  
  Purchase #3 $142.68   4.803%   $149.5329   $149.53   $149.55   $149.50  
  Purchase #4 $242.69   4.476%   $253.5528   $253.55   $253.55   $253.60  
  Purchase #5 $81.55   9.143%   $89.0061   $89.01   $89.00   $89.00  
  Purchase #6 $196.51   6.511%   $209.3048   $209.30   $209.30   $209.30  
  Purchase #7 $179.44   5.138%   $188.6596   $188.66   $188.65   $188.70  
  7 purchase totals = $983.81       $1,044.0295   $1,044.02   $1,044.00   $1,044.10