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 $176.57   8.536%   $191.642   $191.64   $191.65   $191.60  
  Purchase #2 $58.50   5.405%   $61.6619   $61.66   $61.65   $61.70  
  Purchase #3 $169.67   12.551%   $190.9653   $190.97   $190.95   $191.00  
  Purchase #4 $12.76   6.379%   $13.574   $13.57   $13.55   $13.60  
  Purchase #5 $106.93   6.769%   $114.1681   $114.17   $114.15   $114.20  
  Purchase #6 $24.29   5.476%   $25.6201   $25.62   $25.60   $25.60  
  Purchase #7 $19.62   12.387%   $22.0503   $22.05   $22.05   $22.10  
  7 purchase totals = $568.34       $619.6817   $619.68   $619.60   $619.80