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 $177.46   4.758%   $185.9035   $185.90   $185.90   $185.90  
  Purchase #2 $72.97   9.850%   $80.1575   $80.16   $80.15   $80.20  
  Purchase #3 $105.47   7.602%   $113.4878   $113.49   $113.50   $113.50  
  Purchase #4 $159.27   3.375%   $164.6454   $164.65   $164.65   $164.60  
  Purchase #5 $150.65   8.394%   $163.2956   $163.30   $163.30   $163.30  
  Purchase #6 $97.64   8.858%   $106.289   $106.29   $106.30   $106.30  
  Purchase #7 $226.67   5.750%   $239.7035   $239.70   $239.70   $239.70  
  7 purchase totals = $990.13       $1,053.4823   $1,053.49   $1,053.50   $1,053.50