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 $40.84   8.583%   $44.3453   $44.35   $44.35   $44.30  
  Purchase #2 $165.67   6.187%   $175.92   $175.92   $175.90   $175.90  
  Purchase #3 $33.32   4.394%   $34.7841   $34.78   $34.80   $34.80  
  Purchase #4 $76.94   4.406%   $80.33   $80.33   $80.35   $80.30  
  Purchase #5 $233.45   4.409%   $243.7428   $243.74   $243.75   $243.70  
  Purchase #6 $85.39   10.155%   $94.0614   $94.06   $94.05   $94.10  
  Purchase #7 $232.28   5.845%   $245.8568   $245.86   $245.85   $245.90  
  7 purchase totals = $867.89       $919.0404   $919.04   $919.05   $919.00