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 $165.88   10.749%   $183.7104   $183.71   $183.70   $183.70  
  Purchase #2 $182.81   5.751%   $193.3234   $193.32   $193.30   $193.30  
  Purchase #3 $199.83   8.223%   $216.262   $216.26   $216.25   $216.30  
  Purchase #4 $22.78   9.210%   $24.878   $24.88   $24.90   $24.90  
  Purchase #5 $88.46   9.115%   $96.5231   $96.52   $96.50   $96.50  
  Purchase #6 $232.27   12.557%   $261.4361   $261.44   $261.45   $261.40  
  Purchase #7 $220.33   8.505%   $239.0691   $239.07   $239.05   $239.10  
  7 purchase totals = $1,112.36       $1,215.2021   $1,215.20   $1,215.15   $1,215.20