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 $84.27   13.567%   $95.7029   $95.70   $95.70   $95.70  
  Purchase #2 $206.73   3.206%   $213.3578   $213.36   $213.35   $213.40  
  Purchase #3 $165.28   3.608%   $171.2433   $171.24   $171.25   $171.20  
  Purchase #4 $43.42   11.592%   $48.4532   $48.45   $48.45   $48.50  
  Purchase #5 $81.52   12.756%   $91.9187   $91.92   $91.90   $91.90  
  Purchase #6 $229.26   3.245%   $236.6995   $236.70   $236.70   $236.70  
  Purchase #7 $56.38   11.860%   $63.0667   $63.07   $63.05   $63.10  
  7 purchase totals = $866.86       $920.4421   $920.44   $920.40   $920.50