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 $56.54   11.471%   $63.0257   $63.03   $63.05   $63.00  
  Purchase #2 $112.39   5.674%   $118.767   $118.77   $118.75   $118.80  
  Purchase #3 $112.76   10.562%   $124.6697   $124.67   $124.65   $124.70  
  Purchase #4 $190.31   12.615%   $214.3176   $214.32   $214.30   $214.30  
  Purchase #5 $65.93   6.279%   $70.0697   $70.07   $70.05   $70.10  
  Purchase #6 $43.66   8.533%   $47.3855   $47.39   $47.40   $47.40  
  Purchase #7 $183.34   13.667%   $208.3971   $208.40   $208.40   $208.40  
  7 purchase totals = $764.93       $846.6323   $846.65   $846.60   $846.70