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 $249.41   5.726%   $263.6912   $263.69   $263.70   $263.70  
  Purchase #2 $5.70   6.795%   $6.0873   $6.09   $6.10   $6.10  
  Purchase #3 $219.44   11.175%   $243.9624   $243.96   $243.95   $244.00  
  Purchase #4 $143.84   6.836%   $153.6729   $153.67   $153.65   $153.70  
  Purchase #5 $43.60   12.592%   $49.0901   $49.09   $49.10   $49.10  
  Purchase #6 $67.44   3.169%   $69.5772   $69.58   $69.60   $69.60  
  Purchase #7 $225.26   5.167%   $236.8992   $236.90   $236.90   $236.90  
  7 purchase totals = $954.69       $1,022.9803   $1,022.98   $1,023.00   $1,023.10