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 $189.84   3.381%   $196.2585   $196.26   $196.25   $196.30  
  Purchase #2 $199.71   7.821%   $215.3293   $215.33   $215.35   $215.30  
  Purchase #3 $246.44   9.234%   $269.1963   $269.20   $269.20   $269.20  
  Purchase #4 $39.43   11.858%   $44.1056   $44.11   $44.10   $44.10  
  Purchase #5 $167.52   10.851%   $185.6976   $185.70   $185.70   $185.70  
  Purchase #6 $56.30   13.423%   $63.8571   $63.86   $63.85   $63.90  
  Purchase #7 $14.99   13.874%   $17.0697   $17.07   $17.05   $17.10  
  7 purchase totals = $914.23       $991.5141   $991.53   $991.50   $991.60