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 $87.97   5.721%   $93.0028   $93.00   $93.00   $93.00  
  Purchase #2 $233.94   5.372%   $246.5073   $246.51   $246.50   $246.50  
  Purchase #3 $213.34   13.759%   $242.6935   $242.69   $242.70   $242.70  
  Purchase #4 $103.93   9.245%   $113.5383   $113.54   $113.55   $113.50  
  Purchase #5 $59.69   11.210%   $66.3812   $66.38   $66.40   $66.40  
  Purchase #6 $209.56   6.839%   $223.8918   $223.89   $223.90   $223.90  
  Purchase #7 $12.96   5.183%   $13.6317   $13.63   $13.65   $13.60  
  7 purchase totals = $921.39       $999.6466   $999.64   $999.70   $999.60