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 $211.29   3.451%   $218.5816   $218.58   $218.60   $218.60  
  Purchase #2 $230.43   4.766%   $241.4123   $241.41   $241.40   $241.40  
  Purchase #3 $47.26   5.329%   $49.7785   $49.78   $49.80   $49.80  
  Purchase #4 $181.77   6.477%   $193.5432   $193.54   $193.55   $193.50  
  Purchase #5 $174.84   3.286%   $180.5852   $180.59   $180.60   $180.60  
  Purchase #6 $173.94   11.778%   $194.4267   $194.43   $194.45   $194.40  
  Purchase #7 $143.39   10.644%   $158.6524   $158.65   $158.65   $158.70  
  7 purchase totals = $1,162.92       $1,236.9799   $1,236.98   $1,237.05   $1,237.00