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 $67.37   8.222%   $72.9092   $72.91   $72.90   $72.90  
  Purchase #2 $181.69   7.855%   $195.9617   $195.96   $195.95   $196.00  
  Purchase #3 $224.82   8.242%   $243.3497   $243.35   $243.35   $243.30  
  Purchase #4 $217.43   7.688%   $234.146   $234.15   $234.15   $234.10  
  Purchase #5 $164.50   12.583%   $185.199   $185.20   $185.20   $185.20  
  Purchase #6 $149.49   13.364%   $169.4678   $169.47   $169.45   $169.50  
  Purchase #7 $31.68   12.700%   $35.7034   $35.70   $35.70   $35.70  
  7 purchase totals = $1,036.98       $1,136.7368   $1,136.74   $1,136.70   $1,136.70