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 $17.75   7.818%   $19.1377   $19.14   $19.15   $19.10  
  Purchase #2 $78.27   3.300%   $80.8529   $80.85   $80.85   $80.90  
  Purchase #3 $73.55   10.789%   $81.4853   $81.49   $81.50   $81.50  
  Purchase #4 $220.67   8.593%   $239.6322   $239.63   $239.65   $239.60  
  Purchase #5 $142.32   7.730%   $153.3213   $153.32   $153.30   $153.30  
  Purchase #6 $17.86   10.150%   $19.6728   $19.67   $19.65   $19.70  
  Purchase #7 $63.48   7.527%   $68.2581   $68.26   $68.25   $68.30  
  7 purchase totals = $613.90       $662.3603   $662.36   $662.35   $662.40