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 $87.66   10.201%   $96.6022   $96.60   $96.60   $96.60  
  Purchase #2 $218.98   10.257%   $241.4408   $241.44   $241.45   $241.40  
  Purchase #3 $209.47   5.710%   $221.4307   $221.43   $221.45   $221.40  
  Purchase #4 $205.69   9.691%   $225.6234   $225.62   $225.60   $225.60  
  Purchase #5 $11.96   5.783%   $12.6516   $12.65   $12.65   $12.70  
  Purchase #6 $42.78   11.640%   $47.7596   $47.76   $47.75   $47.80  
  Purchase #7 $38.42   8.131%   $41.5439   $41.54   $41.55   $41.50  
  7 purchase totals = $814.96       $887.0522   $887.04   $887.05   $887.00