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 $235.47   13.132%   $266.3919   $266.39   $266.40   $266.40  
  Purchase #2 $195.68   11.423%   $218.0325   $218.03   $218.05   $218.00  
  Purchase #3 $62.54   12.261%   $70.208   $70.21   $70.20   $70.20  
  Purchase #4 $86.97   12.740%   $98.05   $98.05   $98.05   $98.10  
  Purchase #5 $160.39   13.666%   $182.3089   $182.31   $182.30   $182.30  
  Purchase #6 $179.85   11.741%   $200.9662   $200.97   $200.95   $201.00  
  Purchase #7 $189.76   4.854%   $198.971   $198.97   $198.95   $199.00  
  7 purchase totals = $1,110.66       $1,234.9285   $1,234.93   $1,234.90   $1,235.00