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 $169.58   6.157%   $180.021   $180.02   $180.00   $180.00  
  Purchase #2 $165.77   10.784%   $183.6466   $183.65   $183.65   $183.60  
  Purchase #3 $69.40   7.745%   $74.775   $74.78   $74.80   $74.80  
  Purchase #4 $242.62   13.285%   $274.8521   $274.85   $274.85   $274.90  
  Purchase #5 $95.99   7.161%   $102.8638   $102.86   $102.85   $102.90  
  Purchase #6 $85.42   13.168%   $96.6681   $96.67   $96.65   $96.70  
  Purchase #7 $30.63   12.645%   $34.5032   $34.50   $34.50   $34.50  
  7 purchase totals = $859.41       $947.3298   $947.33   $947.30   $947.40