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 $151.94   7.382%   $163.1562   $163.16   $163.15   $163.20  
  Purchase #2 $123.39   10.446%   $136.2793   $136.28   $136.30   $136.30  
  Purchase #3 $65.94   5.395%   $69.4975   $69.50   $69.50   $69.50  
  Purchase #4 $222.67   5.697%   $235.3555   $235.36   $235.35   $235.40  
  Purchase #5 $192.80   12.133%   $216.1924   $216.19   $216.20   $216.20  
  Purchase #6 $152.64   11.129%   $169.6273   $169.63   $169.65   $169.60  
  Purchase #7 $64.48   13.327%   $73.0732   $73.07   $73.05   $73.10  
  7 purchase totals = $973.86       $1,063.1814   $1,063.19   $1,063.20   $1,063.30