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 $34.69   6.678%   $37.0066   $37.01   $37.00   $37.00  
  Purchase #2 $248.28   7.564%   $267.0599   $267.06   $267.05   $267.10  
  Purchase #3 $89.47   9.573%   $98.035   $98.04   $98.05   $98.00  
  Purchase #4 $218.69   12.114%   $245.1821   $245.18   $245.20   $245.20  
  Purchase #5 $85.59   10.737%   $94.7798   $94.78   $94.80   $94.80  
  Purchase #6 $70.99   12.177%   $79.6345   $79.63   $79.65   $79.60  
  Purchase #7 $167.65   3.762%   $173.957   $173.96   $173.95   $174.00  
  7 purchase totals = $915.36       $995.6549   $995.66   $995.70   $995.70