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 $220.59   11.646%   $246.2799   $246.28   $246.30   $246.30  
  Purchase #2 $146.51   3.340%   $151.4034   $151.40   $151.40   $151.40  
  Purchase #3 $245.40   5.601%   $259.1449   $259.14   $259.15   $259.10  
  Purchase #4 $33.26   3.845%   $34.5388   $34.54   $34.55   $34.50  
  Purchase #5 $119.96   4.272%   $125.0847   $125.08   $125.10   $125.10  
  Purchase #6 $179.75   13.255%   $203.5759   $203.58   $203.60   $203.60  
  Purchase #7 $49.55   12.592%   $55.7893   $55.79   $55.80   $55.80  
  7 purchase totals = $995.02       $1,075.8169   $1,075.81   $1,075.90   $1,075.80