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 $247.52   5.454%   $261.0197   $261.02   $261.00   $261.00  
  Purchase #2 $149.77   9.279%   $163.6672   $163.67   $163.65   $163.70  
  Purchase #3 $129.51   3.638%   $134.2216   $134.22   $134.20   $134.20  
  Purchase #4 $95.35   5.411%   $100.5094   $100.51   $100.50   $100.50  
  Purchase #5 $78.29   9.726%   $85.9045   $85.90   $85.90   $85.90  
  Purchase #6 $51.66   10.208%   $56.9335   $56.93   $56.95   $56.90  
  Purchase #7 $189.68   9.257%   $207.2387   $207.24   $207.25   $207.20  
  7 purchase totals = $941.78       $1,009.4946   $1,009.49   $1,009.45   $1,009.40