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 $240.65   11.861%   $269.1935   $269.19   $269.20   $269.20  
  Purchase #2 $66.74   12.187%   $74.8736   $74.87   $74.85   $74.90  
  Purchase #3 $57.38   7.388%   $61.6192   $61.62   $61.60   $61.60  
  Purchase #4 $235.96   12.366%   $265.1388   $265.14   $265.15   $265.10  
  Purchase #5 $102.49   8.576%   $111.2795   $111.28   $111.30   $111.30  
  Purchase #6 $36.44   7.548%   $39.1905   $39.19   $39.20   $39.20  
  Purchase #7 $84.83   6.158%   $90.0538   $90.05   $90.05   $90.10  
  7 purchase totals = $824.49       $911.3489   $911.34   $911.35   $911.40