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 $34.61   3.770%   $35.9148   $35.91   $35.90   $35.90  
  Purchase #2 $179.28   8.536%   $194.5833   $194.58   $194.60   $194.60  
  Purchase #3 $157.56   6.735%   $168.1717   $168.17   $168.15   $168.20  
  Purchase #4 $203.49   7.403%   $218.5544   $218.55   $218.55   $218.60  
  Purchase #5 $140.77   3.356%   $145.4942   $145.49   $145.50   $145.50  
  Purchase #6 $105.99   4.455%   $110.7119   $110.71   $110.70   $110.70  
  Purchase #7 $155.57   7.845%   $167.7745   $167.77   $167.75   $167.80  
  7 purchase totals = $977.27       $1,041.2048   $1,041.18   $1,041.15   $1,041.30