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 $175.63   12.218%   $197.0885   $197.09   $197.10   $197.10  
  Purchase #2 $90.65   6.618%   $96.6492   $96.65   $96.65   $96.60  
  Purchase #3 $135.86   3.253%   $140.2795   $140.28   $140.30   $140.30  
  Purchase #4 $172.46   5.258%   $181.5279   $181.53   $181.55   $181.50  
  Purchase #5 $127.83   11.399%   $142.4013   $142.40   $142.40   $142.40  
  Purchase #6 $198.97   13.266%   $225.3654   $225.37   $225.35   $225.40  
  Purchase #7 $230.54   5.565%   $243.3696   $243.37   $243.35   $243.40  
  7 purchase totals = $1,131.94       $1,226.6814   $1,226.69   $1,226.70   $1,226.70