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 $167.68   5.711%   $177.2562   $177.26   $177.25   $177.30  
  Purchase #2 $25.39   4.737%   $26.5927   $26.59   $26.60   $26.60  
  Purchase #3 $155.26   13.265%   $175.8552   $175.86   $175.85   $175.90  
  Purchase #4 $121.72   10.198%   $134.133   $134.13   $134.15   $134.10  
  Purchase #5 $185.90   13.179%   $210.3998   $210.40   $210.40   $210.40  
  Purchase #6 $38.60   9.289%   $42.1856   $42.19   $42.20   $42.20  
  Purchase #7 $237.31   4.597%   $248.2191   $248.22   $248.20   $248.20  
  7 purchase totals = $931.86       $1,014.6416   $1,014.65   $1,014.65   $1,014.70