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 $38.85   13.496%   $44.0932   $44.09   $44.10   $44.10  
  Purchase #2 $213.59   7.813%   $230.2778   $230.28   $230.30   $230.30  
  Purchase #3 $160.66   5.612%   $169.6762   $169.68   $169.70   $169.70  
  Purchase #4 $200.30   12.655%   $225.648   $225.65   $225.65   $225.60  
  Purchase #5 $26.96   6.358%   $28.6741   $28.67   $28.65   $28.70  
  Purchase #6 $94.81   12.579%   $106.7361   $106.74   $106.75   $106.70  
  Purchase #7 $175.46   6.368%   $186.6333   $186.63   $186.65   $186.60  
  7 purchase totals = $910.63       $991.7387   $991.74   $991.80   $991.70