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 $245.36   13.121%   $277.5537   $277.55   $277.55   $277.60  
  Purchase #2 $144.93   12.362%   $162.8462   $162.85   $162.85   $162.80  
  Purchase #3 $60.31   9.603%   $66.1016   $66.10   $66.10   $66.10  
  Purchase #4 $54.83   5.199%   $57.6806   $57.68   $57.70   $57.70  
  Purchase #5 $230.31   9.704%   $252.6593   $252.66   $252.65   $252.70  
  Purchase #6 $58.25   11.706%   $65.0687   $65.07   $65.05   $65.10  
  Purchase #7 $91.67   9.491%   $100.3704   $100.37   $100.35   $100.40  
  7 purchase totals = $885.66       $982.2805   $982.28   $982.25   $982.40