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 $60.68   13.177%   $68.6758   $68.68   $68.70   $68.70  
  Purchase #2 $141.72   6.216%   $150.5293   $150.53   $150.55   $150.50  
  Purchase #3 $75.35   13.721%   $85.6888   $85.69   $85.70   $85.70  
  Purchase #4 $189.82   4.108%   $197.6178   $197.62   $197.60   $197.60  
  Purchase #5 $250.73   7.385%   $269.2464   $269.25   $269.25   $269.20  
  Purchase #6 $74.53   12.724%   $84.0132   $84.01   $84.00   $84.00  
  Purchase #7 $89.41   5.434%   $94.2685   $94.27   $94.25   $94.30  
  7 purchase totals = $882.24       $950.0398   $950.05   $950.05   $950.00