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 $157.65   11.738%   $176.155   $176.16   $176.15   $176.20  
  Purchase #2 $129.51   11.369%   $144.234   $144.23   $144.25   $144.20  
  Purchase #3 $44.40   9.719%   $48.7152   $48.72   $48.70   $48.70  
  Purchase #4 $236.53   12.608%   $266.3517   $266.35   $266.35   $266.40  
  Purchase #5 $247.35   11.725%   $276.3518   $276.35   $276.35   $276.40  
  Purchase #6 $63.31   8.851%   $68.9136   $68.91   $68.90   $68.90  
  Purchase #7 $205.99   11.655%   $229.9981   $230.00   $230.00   $230.00  
  7 purchase totals = $1,084.74       $1,210.7194   $1,210.72   $1,210.70   $1,210.80