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 $237.72   9.629%   $260.6101   $260.61   $260.60   $260.60  
  Purchase #2 $201.84   7.390%   $216.756   $216.76   $216.75   $216.80  
  Purchase #3 $22.58   6.209%   $23.982   $23.98   $24.00   $24.00  
  Purchase #4 $239.77   13.309%   $271.681   $271.68   $271.70   $271.70  
  Purchase #5 $173.54   11.366%   $193.2646   $193.26   $193.25   $193.30  
  Purchase #6 $141.45   12.762%   $159.5018   $159.50   $159.50   $159.50  
  Purchase #7 $218.34   7.770%   $235.305   $235.31   $235.30   $235.30  
  7 purchase totals = $1,235.24       $1,361.1005   $1,361.10   $1,361.10   $1,361.20