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 $158.59   4.407%   $165.5791   $165.58   $165.60   $165.60  
  Purchase #2 $88.84   6.678%   $94.7727   $94.77   $94.75   $94.80  
  Purchase #3 $59.64   4.770%   $62.4848   $62.48   $62.50   $62.50  
  Purchase #4 $223.86   11.750%   $250.1636   $250.16   $250.15   $250.20  
  Purchase #5 $177.93   9.445%   $194.7355   $194.74   $194.75   $194.70  
  Purchase #6 $86.93   7.616%   $93.5506   $93.55   $93.55   $93.60  
  Purchase #7 $152.26   8.349%   $164.9722   $164.97   $164.95   $165.00  
  7 purchase totals = $948.05       $1,026.2585   $1,026.25   $1,026.25   $1,026.40