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 $103.89   11.824%   $116.174   $116.17   $116.15   $116.20  
  Purchase #2 $53.90   12.701%   $60.7458   $60.75   $60.75   $60.70  
  Purchase #3 $169.97   13.773%   $193.38   $193.38   $193.40   $193.40  
  Purchase #4 $116.50   9.848%   $127.9729   $127.97   $127.95   $128.00  
  Purchase #5 $201.99   12.176%   $226.5843   $226.58   $226.60   $226.60  
  Purchase #6 $117.55   4.163%   $122.4436   $122.44   $122.45   $122.40  
  Purchase #7 $224.72   9.796%   $246.7336   $246.73   $246.75   $246.70  
  7 purchase totals = $988.52       $1,094.0342   $1,094.02   $1,094.05   $1,094.00