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 $44.84   5.631%   $47.3649   $47.36   $47.35   $47.40  
  Purchase #2 $77.55   7.688%   $83.512   $83.51   $83.50   $83.50  
  Purchase #3 $237.89   4.644%   $248.9376   $248.94   $248.95   $248.90  
  Purchase #4 $33.98   3.400%   $35.1353   $35.14   $35.15   $35.10  
  Purchase #5 $178.99   12.830%   $201.9544   $201.95   $201.95   $202.00  
  Purchase #6 $235.82   4.381%   $246.1513   $246.15   $246.15   $246.20  
  Purchase #7 $66.96   7.691%   $72.1099   $72.11   $72.10   $72.10  
  7 purchase totals = $876.03       $935.1654   $935.16   $935.15   $935.20