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 $92.87   5.723%   $98.185   $98.19   $98.20   $98.20  
  Purchase #2 $89.77   8.458%   $97.3627   $97.36   $97.35   $97.40  
  Purchase #3 $175.94   6.157%   $186.7726   $186.77   $186.75   $186.80  
  Purchase #4 $140.80   7.710%   $151.6557   $151.66   $151.65   $151.70  
  Purchase #5 $223.69   5.760%   $236.5745   $236.57   $236.55   $236.60  
  Purchase #6 $181.47   5.862%   $192.1078   $192.11   $192.10   $192.10  
  Purchase #7 $243.69   8.861%   $265.2834   $265.28   $265.30   $265.30  
  7 purchase totals = $1,148.23       $1,227.9417   $1,227.94   $1,227.90   $1,228.10