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 $216.68   3.233%   $223.6853   $223.69   $223.70   $223.70  
  Purchase #2 $138.86   11.336%   $154.6012   $154.60   $154.60   $154.60  
  Purchase #3 $163.86   7.701%   $176.4789   $176.48   $176.50   $176.50  
  Purchase #4 $22.74   10.209%   $25.0615   $25.06   $25.05   $25.10  
  Purchase #5 $237.87   12.827%   $268.3816   $268.38   $268.40   $268.40  
  Purchase #6 $114.52   7.762%   $123.409   $123.41   $123.40   $123.40  
  Purchase #7 $36.73   7.539%   $39.4991   $39.50   $39.50   $39.50  
  7 purchase totals = $931.26       $1,011.1166   $1,011.12   $1,011.15   $1,011.20