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 $238.33   12.783%   $268.7957   $268.80   $268.80   $268.80  
  Purchase #2 $210.25   10.789%   $232.9339   $232.93   $232.95   $232.90  
  Purchase #3 $230.42   13.871%   $262.3816   $262.38   $262.40   $262.40  
  Purchase #4 $127.35   3.144%   $131.3539   $131.35   $131.35   $131.40  
  Purchase #5 $10.39   9.743%   $11.4023   $11.40   $11.40   $11.40  
  Purchase #6 $49.48   11.763%   $55.3003   $55.30   $55.30   $55.30  
  Purchase #7 $125.33   8.464%   $135.9379   $135.94   $135.95   $135.90  
  7 purchase totals = $991.55       $1,098.1056   $1,098.10   $1,098.15   $1,098.10