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 $86.79   13.260%   $98.2984   $98.30   $98.30   $98.30  
  Purchase #2 $183.48   9.242%   $200.4372   $200.44   $200.45   $200.40  
  Purchase #3 $143.49   7.198%   $153.8184   $153.82   $153.80   $153.80  
  Purchase #4 $239.40   10.716%   $265.0541   $265.05   $265.05   $265.10  
  Purchase #5 $225.93   4.651%   $236.438   $236.44   $236.45   $236.40  
  Purchase #6 $189.82   8.148%   $205.2865   $205.29   $205.30   $205.30  
  Purchase #7 $71.49   4.320%   $74.5784   $74.58   $74.60   $74.60  
  7 purchase totals = $1,140.40       $1,233.9110   $1,233.92   $1,233.95   $1,233.90