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 $176.36   13.258%   $199.7418   $199.74   $199.75   $199.70  
  Purchase #2 $43.58   11.294%   $48.5019   $48.50   $48.50   $48.50  
  Purchase #3 $65.26   3.631%   $67.6296   $67.63   $67.65   $67.60  
  Purchase #4 $248.28   8.859%   $270.2751   $270.28   $270.30   $270.30  
  Purchase #5 $78.68   9.254%   $85.961   $85.96   $85.95   $86.00  
  Purchase #6 $90.91   8.568%   $98.6992   $98.70   $98.70   $98.70  
  Purchase #7 $206.50   11.709%   $230.6791   $230.68   $230.70   $230.70  
  7 purchase totals = $909.57       $1,001.4877   $1,001.49   $1,001.55   $1,001.50