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 $57.39   5.476%   $60.5327   $60.53   $60.55   $60.50  
  Purchase #2 $48.76   12.545%   $54.8769   $54.88   $54.90   $54.90  
  Purchase #3 $233.69   3.359%   $241.5396   $241.54   $241.55   $241.50  
  Purchase #4 $84.77   12.642%   $95.4866   $95.49   $95.50   $95.50  
  Purchase #5 $159.63   13.808%   $181.6717   $181.67   $181.65   $181.70  
  Purchase #6 $43.45   4.207%   $45.2779   $45.28   $45.30   $45.30  
  Purchase #7 $184.50   7.629%   $198.5755   $198.58   $198.60   $198.60  
  7 purchase totals = $812.19       $877.9609   $877.97   $878.05   $878.00