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 $31.71   12.623%   $35.7128   $35.71   $35.70   $35.70  
  Purchase #2 $220.82   11.301%   $245.7749   $245.77   $245.75   $245.80  
  Purchase #3 $184.75   11.372%   $205.7598   $205.76   $205.75   $205.80  
  Purchase #4 $35.30   11.139%   $39.2321   $39.23   $39.25   $39.20  
  Purchase #5 $117.54   9.241%   $128.4019   $128.40   $128.40   $128.40  
  Purchase #6 $163.25   3.708%   $169.3033   $169.30   $169.30   $169.30  
  Purchase #7 $73.61   11.276%   $81.9103   $81.91   $81.90   $81.90  
  7 purchase totals = $826.98       $906.0951   $906.08   $906.05   $906.10