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 $240.62   9.516%   $263.5174   $263.52   $263.50   $263.50  
  Purchase #2 $106.31   6.660%   $113.3902   $113.39   $113.40   $113.40  
  Purchase #3 $174.81   6.566%   $186.288   $186.29   $186.30   $186.30  
  Purchase #4 $210.63   13.435%   $238.9281   $238.93   $238.95   $238.90  
  Purchase #5 $165.91   4.427%   $173.2548   $173.25   $173.25   $173.30  
  Purchase #6 $180.69   10.458%   $199.5866   $199.59   $199.60   $199.60  
  Purchase #7 $183.55   10.184%   $202.2427   $202.24   $202.25   $202.20  
  7 purchase totals = $1,262.52       $1,377.2078   $1,377.21   $1,377.25   $1,377.20