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 $107.49   10.739%   $119.0334   $119.03   $119.05   $119.00  
  Purchase #2 $99.58   4.587%   $104.1477   $104.15   $104.15   $104.10  
  Purchase #3 $96.39   7.632%   $103.7465   $103.75   $103.75   $103.70  
  Purchase #4 $13.57   4.507%   $14.1816   $14.18   $14.20   $14.20  
  Purchase #5 $115.70   6.261%   $122.944   $122.94   $122.95   $122.90  
  Purchase #6 $12.92   8.454%   $14.0123   $14.01   $14.00   $14.00  
  Purchase #7 $16.51   11.405%   $18.393   $18.39   $18.40   $18.40  
  7 purchase totals = $462.16       $496.4585   $496.45   $496.50   $496.30