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 $193.95   12.236%   $217.6817   $217.68   $217.70   $217.70  
  Purchase #2 $214.56   13.628%   $243.8002   $243.80   $243.80   $243.80  
  Purchase #3 $67.45   7.748%   $72.676   $72.68   $72.70   $72.70  
  Purchase #4 $111.91   12.681%   $126.1013   $126.10   $126.10   $126.10  
  Purchase #5 $213.66   5.535%   $225.4861   $225.49   $225.50   $225.50  
  Purchase #6 $148.92   3.824%   $154.6147   $154.61   $154.60   $154.60  
  Purchase #7 $130.41   8.317%   $141.2562   $141.26   $141.25   $141.30  
  7 purchase totals = $1,080.86       $1,181.6162   $1,181.62   $1,181.65   $1,181.70