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 $58.38   12.218%   $65.5129   $65.51   $65.50   $65.50  
  Purchase #2 $21.35   5.577%   $22.5407   $22.54   $22.55   $22.50  
  Purchase #3 $159.53   12.651%   $179.7121   $179.71   $179.70   $179.70  
  Purchase #4 $199.62   12.466%   $224.5046   $224.50   $224.50   $224.50  
  Purchase #5 $196.58   7.602%   $211.524   $211.52   $211.50   $211.50  
  Purchase #6 $31.89   11.852%   $35.6696   $35.67   $35.65   $35.70  
  Purchase #7 $227.64   13.178%   $257.6384   $257.64   $257.65   $257.60  
  7 purchase totals = $894.99       $997.1023   $997.09   $997.05   $997.00