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 $246.37   13.109%   $278.6666   $278.67   $278.65   $278.70  
  Purchase #2 $176.92   3.492%   $183.098   $183.10   $183.10   $183.10  
  Purchase #3 $97.35   3.233%   $100.4973   $100.50   $100.50   $100.50  
  Purchase #4 $231.30   9.199%   $252.5773   $252.58   $252.60   $252.60  
  Purchase #5 $188.30   7.786%   $202.961   $202.96   $202.95   $203.00  
  Purchase #6 $136.30   7.562%   $146.607   $146.61   $146.60   $146.60  
  Purchase #7 $185.99   7.594%   $200.1141   $200.11   $200.10   $200.10  
  7 purchase totals = $1,262.53       $1,364.5213   $1,364.53   $1,364.50   $1,364.60