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 $233.85   11.697%   $261.2034   $261.20   $261.20   $261.20  
  Purchase #2 $97.54   9.189%   $106.503   $106.50   $106.50   $106.50  
  Purchase #3 $38.96   10.629%   $43.1011   $43.10   $43.10   $43.10  
  Purchase #4 $6.45   13.599%   $7.3271   $7.33   $7.35   $7.30  
  Purchase #5 $67.93   5.775%   $71.853   $71.85   $71.85   $71.90  
  Purchase #6 $177.34   6.610%   $189.0622   $189.06   $189.05   $189.10  
  Purchase #7 $212.88   9.829%   $233.804   $233.80   $233.80   $233.80  
  7 purchase totals = $834.95       $912.8538   $912.84   $912.85   $912.90