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 $205.49   8.813%   $223.5998   $223.60   $223.60   $223.60  
  Purchase #2 $248.93   11.113%   $276.5936   $276.59   $276.60   $276.60  
  Purchase #3 $73.34   11.158%   $81.5233   $81.52   $81.50   $81.50  
  Purchase #4 $93.30   5.337%   $98.2794   $98.28   $98.30   $98.30  
  Purchase #5 $7.73   8.840%   $8.4133   $8.41   $8.40   $8.40  
  Purchase #6 $216.42   11.201%   $240.6612   $240.66   $240.65   $240.70  
  Purchase #7 $58.51   13.167%   $66.214   $66.21   $66.20   $66.20  
  7 purchase totals = $903.72       $995.2846   $995.27   $995.25   $995.30