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 $202.59   5.618%   $213.9715   $213.97   $213.95   $214.00  
  Purchase #2 $115.37   8.557%   $125.2422   $125.24   $125.25   $125.20  
  Purchase #3 $32.52   7.115%   $34.8338   $34.83   $34.85   $34.80  
  Purchase #4 $221.61   12.791%   $249.9561   $249.96   $249.95   $250.00  
  Purchase #5 $167.50   6.227%   $177.9302   $177.93   $177.95   $177.90  
  Purchase #6 $126.71   11.730%   $141.5731   $141.57   $141.55   $141.60  
  Purchase #7 $97.32   10.470%   $107.5094   $107.51   $107.50   $107.50  
  7 purchase totals = $963.62       $1,051.0163   $1,051.01   $1,051.00   $1,051.00