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 $61.58   8.435%   $66.7743   $66.77   $66.75   $66.80  
  Purchase #2 $228.99   5.744%   $242.1432   $242.14   $242.15   $242.10  
  Purchase #3 $171.45   9.585%   $187.8835   $187.88   $187.90   $187.90  
  Purchase #4 $22.98   4.390%   $23.9888   $23.99   $24.00   $24.00  
  Purchase #5 $111.68   6.279%   $118.6924   $118.69   $118.70   $118.70  
  Purchase #6 $180.42   6.483%   $192.1166   $192.12   $192.10   $192.10  
  Purchase #7 $207.30   5.548%   $218.801   $218.80   $218.80   $218.80  
  7 purchase totals = $984.40       $1,050.3998   $1,050.39   $1,050.40   $1,050.40