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 $242.84   13.781%   $276.3058   $276.31   $276.30   $276.30  
  Purchase #2 $23.82   6.681%   $25.4114   $25.41   $25.40   $25.40  
  Purchase #3 $112.58   13.235%   $127.48   $127.48   $127.50   $127.50  
  Purchase #4 $190.94   12.596%   $214.9908   $214.99   $215.00   $215.00  
  Purchase #5 $167.40   3.618%   $173.4565   $173.46   $173.45   $173.50  
  Purchase #6 $212.42   6.541%   $226.3144   $226.31   $226.30   $226.30  
  Purchase #7 $23.96   5.795%   $25.3485   $25.35   $25.35   $25.30  
  7 purchase totals = $973.96       $1,069.3074   $1,069.31   $1,069.30   $1,069.30