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 $149.97   8.759%   $163.1059   $163.11   $163.10   $163.10  
  Purchase #2 $58.58   7.396%   $62.9126   $62.91   $62.90   $62.90  
  Purchase #3 $88.69   7.548%   $95.3843   $95.38   $95.40   $95.40  
  Purchase #4 $163.95   8.283%   $177.53   $177.53   $177.55   $177.50  
  Purchase #5 $208.55   12.113%   $233.8117   $233.81   $233.80   $233.80  
  Purchase #6 $84.64   12.852%   $95.5179   $95.52   $95.50   $95.50  
  Purchase #7 $127.50   8.176%   $137.9244   $137.92   $137.90   $137.90  
  7 purchase totals = $881.88       $966.1868   $966.18   $966.15   $966.10