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 $225.58   12.381%   $253.5091   $253.51   $253.50   $253.50  
  Purchase #2 $197.32   11.525%   $220.0611   $220.06   $220.05   $220.10  
  Purchase #3 $96.28   11.197%   $107.0605   $107.06   $107.05   $107.10  
  Purchase #4 $6.32   6.802%   $6.7499   $6.75   $6.75   $6.70  
  Purchase #5 $238.84   5.163%   $251.1713   $251.17   $251.15   $251.20  
  Purchase #6 $186.74   5.131%   $196.3216   $196.32   $196.30   $196.30  
  Purchase #7 $95.72   3.204%   $98.7869   $98.79   $98.80   $98.80  
  7 purchase totals = $1,046.80       $1,133.6604   $1,133.66   $1,133.60   $1,133.70