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 $152.35   8.794%   $165.7477   $165.75   $165.75   $165.70  
  Purchase #2 $225.36   6.643%   $240.3307   $240.33   $240.35   $240.30  
  Purchase #3 $23.81   6.626%   $25.3877   $25.39   $25.40   $25.40  
  Purchase #4 $64.29   12.528%   $72.3443   $72.34   $72.35   $72.30  
  Purchase #5 $175.94   13.359%   $199.4438   $199.44   $199.45   $199.40  
  Purchase #6 $187.71   12.848%   $211.827   $211.83   $211.85   $211.80  
  Purchase #7 $29.69   3.848%   $30.8325   $30.83   $30.85   $30.80  
  7 purchase totals = $859.15       $945.9137   $945.91   $946.00   $945.70