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 $239.86   11.558%   $267.583   $267.58   $267.60   $267.60  
  Purchase #2 $60.25   5.442%   $63.5288   $63.53   $63.55   $63.50  
  Purchase #3 $173.85   7.773%   $187.3634   $187.36   $187.35   $187.40  
  Purchase #4 $209.38   4.781%   $219.3905   $219.39   $219.40   $219.40  
  Purchase #5 $197.83   4.767%   $207.2606   $207.26   $207.25   $207.30  
  Purchase #6 $197.94   12.654%   $222.9873   $222.99   $223.00   $223.00  
  Purchase #7 $50.58   13.471%   $57.3936   $57.39   $57.40   $57.40  
  7 purchase totals = $1,129.69       $1,225.5072   $1,225.50   $1,225.55   $1,225.60