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 $207.84   9.114%   $226.7825   $226.78   $226.80   $226.80  
  Purchase #2 $134.93   10.407%   $148.9722   $148.97   $148.95   $149.00  
  Purchase #3 $124.87   9.869%   $137.1934   $137.19   $137.20   $137.20  
  Purchase #4 $241.89   6.657%   $257.9926   $257.99   $258.00   $258.00  
  Purchase #5 $23.94   11.635%   $26.7254   $26.73   $26.75   $26.70  
  Purchase #6 $60.81   11.739%   $67.9485   $67.95   $67.95   $67.90  
  Purchase #7 $91.99   4.508%   $96.1369   $96.14   $96.15   $96.10  
  7 purchase totals = $886.27       $961.7515   $961.75   $961.80   $961.70