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 $96.41   5.848%   $102.0481   $102.05   $102.05   $102.00  
  Purchase #2 $230.95   9.652%   $253.2413   $253.24   $253.25   $253.20  
  Purchase #3 $127.98   13.814%   $145.6592   $145.66   $145.65   $145.70  
  Purchase #4 $161.63   10.784%   $179.0602   $179.06   $179.05   $179.10  
  Purchase #5 $153.62   13.479%   $174.3264   $174.33   $174.35   $174.30  
  Purchase #6 $72.59   9.196%   $79.2654   $79.27   $79.25   $79.30  
  Purchase #7 $106.38   12.337%   $119.5041   $119.50   $119.50   $119.50  
  7 purchase totals = $949.56       $1,053.1047   $1,053.11   $1,053.10   $1,053.10