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 $48.96   8.677%   $53.2083   $53.21   $53.20   $53.20  
  Purchase #2 $248.37   6.542%   $264.6184   $264.62   $264.60   $264.60  
  Purchase #3 $64.76   10.534%   $71.5818   $71.58   $71.60   $71.60  
  Purchase #4 $86.58   12.304%   $97.2328   $97.23   $97.25   $97.20  
  Purchase #5 $204.67   13.384%   $232.063   $232.06   $232.05   $232.10  
  Purchase #6 $91.34   8.506%   $99.1094   $99.11   $99.10   $99.10  
  Purchase #7 $173.81   9.713%   $190.6922   $190.69   $190.70   $190.70  
  7 purchase totals = $918.49       $1,008.5059   $1,008.50   $1,008.50   $1,008.50