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 $248.95   7.394%   $267.3574   $267.36   $267.35   $267.40  
  Purchase #2 $55.27   9.416%   $60.4742   $60.47   $60.45   $60.50  
  Purchase #3 $124.62   9.134%   $136.0028   $136.00   $136.00   $136.00  
  Purchase #4 $123.81   3.572%   $128.2325   $128.23   $128.25   $128.20  
  Purchase #5 $84.78   6.220%   $90.0533   $90.05   $90.05   $90.10  
  Purchase #6 $147.29   4.754%   $154.2922   $154.29   $154.30   $154.30  
  Purchase #7 $43.41   13.265%   $49.1683   $49.17   $49.15   $49.20  
  7 purchase totals = $828.13       $885.5807   $885.57   $885.55   $885.70