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 $173.90   5.463%   $183.4002   $183.40   $183.40   $183.40  
  Purchase #2 $19.56   12.627%   $22.0298   $22.03   $22.05   $22.00  
  Purchase #3 $197.38   4.179%   $205.6285   $205.63   $205.65   $205.60  
  Purchase #4 $234.76   9.794%   $257.7524   $257.75   $257.75   $257.80  
  Purchase #5 $89.90   3.782%   $93.3   $93.30   $93.30   $93.30  
  Purchase #6 $198.63   4.476%   $207.5207   $207.52   $207.50   $207.50  
  Purchase #7 $31.52   10.644%   $34.875   $34.88   $34.90   $34.90  
  7 purchase totals = $945.65       $1,004.5066   $1,004.51   $1,004.55   $1,004.50