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 $169.92   3.774%   $176.3328   $176.33   $176.35   $176.30  
  Purchase #2 $177.44   9.161%   $193.6953   $193.70   $193.70   $193.70  
  Purchase #3 $229.90   8.164%   $248.669   $248.67   $248.65   $248.70  
  Purchase #4 $30.69   7.179%   $32.8932   $32.89   $32.90   $32.90  
  Purchase #5 $145.34   3.386%   $150.2612   $150.26   $150.25   $150.30  
  Purchase #6 $49.55   9.745%   $54.3786   $54.38   $54.40   $54.40  
  Purchase #7 $69.28   3.475%   $71.6875   $71.69   $71.70   $71.70  
  7 purchase totals = $872.12       $927.9176   $927.92   $927.95   $928.00