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 $136.83   5.663%   $144.5787   $144.58   $144.60   $144.60  
  Purchase #2 $239.97   12.325%   $269.5463   $269.55   $269.55   $269.50  
  Purchase #3 $78.58   5.832%   $83.1628   $83.16   $83.15   $83.20  
  Purchase #4 $77.64   10.783%   $86.0119   $86.01   $86.00   $86.00  
  Purchase #5 $202.28   11.426%   $225.3925   $225.39   $225.40   $225.40  
  Purchase #6 $237.32   10.581%   $262.4308   $262.43   $262.45   $262.40  
  Purchase #7 $153.83   7.457%   $165.3011   $165.30   $165.30   $165.30  
  7 purchase totals = $1,126.45       $1,236.4241   $1,236.42   $1,236.45   $1,236.40