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 $246.58   6.482%   $262.5633   $262.56   $262.55   $262.60  
  Purchase #2 $39.92   11.651%   $44.5711   $44.57   $44.55   $44.60  
  Purchase #3 $139.91   5.502%   $147.6078   $147.61   $147.60   $147.60  
  Purchase #4 $152.40   11.620%   $170.1089   $170.11   $170.10   $170.10  
  Purchase #5 $238.84   3.176%   $246.4256   $246.43   $246.45   $246.40  
  Purchase #6 $237.51   13.239%   $268.9539   $268.95   $268.95   $269.00  
  Purchase #7 $171.69   10.812%   $190.2531   $190.25   $190.25   $190.30  
  7 purchase totals = $1,226.85       $1,330.4837   $1,330.48   $1,330.45   $1,330.60