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 $24.54   12.335%   $27.567   $27.57   $27.55   $27.60  
  Purchase #2 $206.59   5.824%   $218.6218   $218.62   $218.60   $218.60  
  Purchase #3 $73.44   3.601%   $76.0846   $76.08   $76.10   $76.10  
  Purchase #4 $219.61   4.600%   $229.7121   $229.71   $229.70   $229.70  
  Purchase #5 $162.71   5.812%   $172.1667   $172.17   $172.15   $172.20  
  Purchase #6 $101.51   9.149%   $110.7971   $110.80   $110.80   $110.80  
  Purchase #7 $207.41   3.349%   $214.3562   $214.36   $214.35   $214.40  
  7 purchase totals = $995.81       $1,049.3055   $1,049.31   $1,049.25   $1,049.40