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 $241.50   4.873%   $253.2683   $253.27   $253.25   $253.30  
  Purchase #2 $26.95   9.119%   $29.4076   $29.41   $29.40   $29.40  
  Purchase #3 $118.96   5.270%   $125.2292   $125.23   $125.25   $125.20  
  Purchase #4 $202.45   9.672%   $222.031   $222.03   $222.05   $222.00  
  Purchase #5 $143.83   12.517%   $161.8332   $161.83   $161.85   $161.80  
  Purchase #6 $68.30   7.490%   $73.4157   $73.42   $73.40   $73.40  
  Purchase #7 $130.30   8.189%   $140.9703   $140.97   $140.95   $141.00  
  7 purchase totals = $932.29       $1,006.1553   $1,006.16   $1,006.15   $1,006.10