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 $188.34   6.732%   $201.019   $201.02   $201.00   $201.00  
  Purchase #2 $36.72   6.133%   $38.972   $38.97   $38.95   $39.00  
  Purchase #3 $227.51   5.688%   $240.4508   $240.45   $240.45   $240.50  
  Purchase #4 $220.99   4.621%   $231.2019   $231.20   $231.20   $231.20  
  Purchase #5 $37.38   8.428%   $40.5304   $40.53   $40.55   $40.50  
  Purchase #6 $109.92   4.394%   $114.7499   $114.75   $114.75   $114.70  
  Purchase #7 $224.59   7.833%   $242.1821   $242.18   $242.20   $242.20  
  7 purchase totals = $1,045.45       $1,109.1061   $1,109.10   $1,109.10   $1,109.10