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 $210.88   11.554%   $235.2451   $235.25   $235.25   $235.20  
  Purchase #2 $25.77   4.663%   $26.9717   $26.97   $26.95   $27.00  
  Purchase #3 $32.58   10.573%   $36.0247   $36.02   $36.00   $36.00  
  Purchase #4 $197.42   6.397%   $210.049   $210.05   $210.05   $210.00  
  Purchase #5 $248.81   7.279%   $266.9209   $266.92   $266.90   $266.90  
  Purchase #6 $107.58   7.348%   $115.485   $115.49   $115.50   $115.50  
  Purchase #7 $167.34   11.802%   $187.0895   $187.09   $187.10   $187.10  
  7 purchase totals = $990.38       $1,077.7859   $1,077.79   $1,077.75   $1,077.70