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 $190.25   10.207%   $209.6688   $209.67   $209.65   $209.70  
  Purchase #2 $45.98   5.463%   $48.4919   $48.49   $48.50   $48.50  
  Purchase #3 $10.31   12.109%   $11.5584   $11.56   $11.55   $11.60  
  Purchase #4 $104.62   9.190%   $114.2346   $114.23   $114.25   $114.20  
  Purchase #5 $112.75   5.553%   $119.011   $119.01   $119.00   $119.00  
  Purchase #6 $156.38   11.265%   $173.9962   $174.00   $174.00   $174.00  
  Purchase #7 $219.60   12.304%   $246.6196   $246.62   $246.60   $246.60  
  7 purchase totals = $839.89       $923.5805   $923.58   $923.55   $923.60