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 $120.98   10.791%   $134.035   $134.04   $134.05   $134.00  
  Purchase #2 $111.57   5.307%   $117.491   $117.49   $117.50   $117.50  
  Purchase #3 $52.45   6.208%   $55.7061   $55.71   $55.70   $55.70  
  Purchase #4 $151.41   9.684%   $166.0725   $166.07   $166.05   $166.10  
  Purchase #5 $47.38   5.270%   $49.8769   $49.88   $49.90   $49.90  
  Purchase #6 $239.79   8.345%   $259.8005   $259.80   $259.80   $259.80  
  Purchase #7 $181.84   5.733%   $192.2649   $192.26   $192.25   $192.30  
  7 purchase totals = $905.42       $975.2469   $975.25   $975.25   $975.30