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 $88.39   6.616%   $94.2379   $94.24   $94.25   $94.20  
  Purchase #2 $239.77   13.719%   $272.664   $272.66   $272.65   $272.70  
  Purchase #3 $224.73   9.320%   $245.6748   $245.67   $245.65   $245.70  
  Purchase #4 $101.70   4.394%   $106.1687   $106.17   $106.15   $106.20  
  Purchase #5 $220.53   3.129%   $227.4304   $227.43   $227.45   $227.40  
  Purchase #6 $158.33   12.108%   $177.5006   $177.50   $177.50   $177.50  
  Purchase #7 $163.81   6.857%   $175.0425   $175.04   $175.05   $175.00  
  7 purchase totals = $1,197.26       $1,298.7189   $1,298.71   $1,298.70   $1,298.70