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 $56.72   4.827%   $59.4579   $59.46   $59.45   $59.50  
  Purchase #2 $181.76   8.813%   $197.7785   $197.78   $197.80   $197.80  
  Purchase #3 $211.37   4.769%   $221.4502   $221.45   $221.45   $221.50  
  Purchase #4 $30.60   12.846%   $34.5309   $34.53   $34.55   $34.50  
  Purchase #5 $233.30   7.690%   $251.2408   $251.24   $251.25   $251.20  
  Purchase #6 $229.31   11.661%   $256.0498   $256.05   $256.05   $256.00  
  Purchase #7 $164.50   13.123%   $186.0873   $186.09   $186.10   $186.10  
  7 purchase totals = $1,107.56       $1,206.5954   $1,206.60   $1,206.65   $1,206.60