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 $170.93   9.267%   $186.7701   $186.77   $186.75   $186.80  
  Purchase #2 $233.82   3.306%   $241.5501   $241.55   $241.55   $241.60  
  Purchase #3 $169.92   11.833%   $190.0266   $190.03   $190.05   $190.00  
  Purchase #4 $151.62   11.657%   $169.2943   $169.29   $169.30   $169.30  
  Purchase #5 $69.28   10.560%   $76.596   $76.60   $76.60   $76.60  
  Purchase #6 $206.57   5.617%   $218.173   $218.17   $218.15   $218.20  
  Purchase #7 $189.58   13.351%   $214.8908   $214.89   $214.90   $214.90  
  7 purchase totals = $1,191.72       $1,297.3009   $1,297.30   $1,297.30   $1,297.40