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 $241.77   10.699%   $267.637   $267.64   $267.65   $267.60  
  Purchase #2 $34.61   3.602%   $35.8567   $35.86   $35.85   $35.90  
  Purchase #3 $218.31   5.291%   $229.8608   $229.86   $229.85   $229.90  
  Purchase #4 $122.65   9.434%   $134.2208   $134.22   $134.20   $134.20  
  Purchase #5 $130.34   8.670%   $141.6405   $141.64   $141.65   $141.60  
  Purchase #6 $117.82   3.517%   $121.9637   $121.96   $121.95   $122.00  
  Purchase #7 $120.96   7.246%   $129.7248   $129.72   $129.70   $129.70  
  7 purchase totals = $986.46       $1,060.9043   $1,060.90   $1,060.85   $1,060.90