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 $135.59   12.874%   $153.0459   $153.05   $153.05   $153.00  
  Purchase #2 $234.83   13.131%   $265.6655   $265.67   $265.65   $265.70  
  Purchase #3 $168.99   12.602%   $190.2861   $190.29   $190.30   $190.30  
  Purchase #4 $43.57   5.460%   $45.9489   $45.95   $45.95   $45.90  
  Purchase #5 $154.87   5.360%   $163.171   $163.17   $163.15   $163.20  
  Purchase #6 $188.57   13.658%   $214.3249   $214.32   $214.30   $214.30  
  Purchase #7 $96.51   12.760%   $108.8247   $108.82   $108.80   $108.80  
  7 purchase totals = $1,022.93       $1,141.2670   $1,141.27   $1,141.20   $1,141.20