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 $149.87   13.158%   $169.5899   $169.59   $169.60   $169.60  
  Purchase #2 $197.26   3.765%   $204.6868   $204.69   $204.70   $204.70  
  Purchase #3 $235.68   13.214%   $266.8228   $266.82   $266.80   $266.80  
  Purchase #4 $72.36   4.513%   $75.6256   $75.63   $75.65   $75.60  
  Purchase #5 $196.37   5.282%   $206.7423   $206.74   $206.75   $206.70  
  Purchase #6 $35.95   5.577%   $37.9549   $37.95   $37.95   $38.00  
  Purchase #7 $231.49   11.272%   $257.5836   $257.58   $257.60   $257.60  
  7 purchase totals = $1,118.98       $1,219.0059   $1,219.00   $1,219.05   $1,219.00