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 $163.96   11.702%   $183.1466   $183.15   $183.15   $183.10  
  Purchase #2 $173.43   9.188%   $189.3647   $189.36   $189.35   $189.40  
  Purchase #3 $145.45   11.635%   $162.3731   $162.37   $162.35   $162.40  
  Purchase #4 $230.76   12.449%   $259.4873   $259.49   $259.50   $259.50  
  Purchase #5 $141.87   7.700%   $152.794   $152.79   $152.80   $152.80  
  Purchase #6 $133.48   13.641%   $151.688   $151.69   $151.70   $151.70  
  Purchase #7 $136.43   8.636%   $148.2121   $148.21   $148.20   $148.20  
  7 purchase totals = $1,125.38       $1,247.0658   $1,247.06   $1,247.05   $1,247.10