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 $54.97   9.783%   $60.3477   $60.35   $60.35   $60.30  
  Purchase #2 $248.74   13.110%   $281.3498   $281.35   $281.35   $281.30  
  Purchase #3 $61.34   4.265%   $63.9562   $63.96   $63.95   $64.00  
  Purchase #4 $206.80   6.496%   $220.2337   $220.23   $220.25   $220.20  
  Purchase #5 $126.52   8.469%   $137.235   $137.24   $137.25   $137.20  
  Purchase #6 $89.49   3.215%   $92.3671   $92.37   $92.35   $92.40  
  Purchase #7 $217.31   7.233%   $233.028   $233.03   $233.05   $233.00  
  7 purchase totals = $1,005.17       $1,088.5175   $1,088.53   $1,088.55   $1,088.40