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 $239.39   10.814%   $265.2776   $265.28   $265.30   $265.30  
  Purchase #2 $148.37   12.258%   $166.5572   $166.56   $166.55   $166.60  
  Purchase #3 $107.99   5.388%   $113.8085   $113.81   $113.80   $113.80  
  Purchase #4 $97.64   3.388%   $100.948   $100.95   $100.95   $100.90  
  Purchase #5 $241.89   7.500%   $260.0318   $260.03   $260.05   $260.00  
  Purchase #6 $165.49   12.319%   $185.8767   $185.88   $185.90   $185.90  
  Purchase #7 $165.52   6.727%   $176.6545   $176.65   $176.65   $176.70  
  7 purchase totals = $1,166.29       $1,269.1543   $1,269.16   $1,269.20   $1,269.20