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 $56.50   6.596%   $60.2267   $60.23   $60.25   $60.20  
  Purchase #2 $122.53   11.139%   $136.1786   $136.18   $136.20   $136.20  
  Purchase #3 $145.75   5.514%   $153.7867   $153.79   $153.80   $153.80  
  Purchase #4 $146.62   7.244%   $157.2412   $157.24   $157.25   $157.20  
  Purchase #5 $10.35   13.148%   $11.7108   $11.71   $11.70   $11.70  
  Purchase #6 $46.64   7.137%   $49.9687   $49.97   $49.95   $50.00  
  Purchase #7 $149.85   11.665%   $167.33   $167.33   $167.35   $167.30  
  7 purchase totals = $678.24       $736.4427   $736.45   $736.50   $736.40