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 $177.58   11.834%   $198.5948   $198.59   $198.60   $198.60  
  Purchase #2 $55.28   10.132%   $60.881   $60.88   $60.90   $60.90  
  Purchase #3 $211.66   11.791%   $236.6168   $236.62   $236.60   $236.60  
  Purchase #4 $25.50   12.146%   $28.5972   $28.60   $28.60   $28.60  
  Purchase #5 $152.42   10.386%   $168.2503   $168.25   $168.25   $168.30  
  Purchase #6 $48.58   10.249%   $53.559   $53.56   $53.55   $53.60  
  Purchase #7 $68.25   11.113%   $75.8346   $75.83   $75.85   $75.80  
  7 purchase totals = $739.27       $822.3337   $822.33   $822.35   $822.40