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 $62.62   5.631%   $66.1461   $66.15   $66.15   $66.10  
  Purchase #2 $129.65   8.836%   $141.1059   $141.11   $141.10   $141.10  
  Purchase #3 $151.83   3.133%   $156.5868   $156.59   $156.60   $156.60  
  Purchase #4 $208.35   5.608%   $220.0343   $220.03   $220.05   $220.00  
  Purchase #5 $66.42   5.201%   $69.8745   $69.87   $69.85   $69.90  
  Purchase #6 $46.67   5.219%   $49.1057   $49.11   $49.10   $49.10  
  Purchase #7 $130.32   7.732%   $140.3963   $140.40   $140.40   $140.40  
  7 purchase totals = $795.86       $843.2496   $843.26   $843.25   $843.20